[PATCH v2 0/3] arm64/sve: Fix mutating register endianness on big-endian

[PATCH v2 0/3] arm64/sve: Fix mutating register endianness on big-endian

[Dave Martin]

This is a respin of [1], swapping the first two patches so that (new)
patch 1 can go to stable stand-alone without depending on patch 2.

I've also smuggled in a new trivial patch 3, that just replaces a
couple of magic numbers for which there is now a suitable #define to
use, which have been bugging me for a while.

Original blurb:

By inspection while debugging something else, I noticed that the byte
order of FPSIMD V-register stores and SVE Z-register stores is not the
same when running on big-endian.

This is not properly taken into account when moving between the FPSIMD
and SVE register views inside the kernel, resulting in the bytes of a
V-register getting spontaneously reversed in some situations, from
userspace's point of view.  The signal frame and ptrace interface are
also affected.  The KVM ABI forbids mixing the two views and so should
not be affected.

See patch 2 for details.

Patch 1 does some trivial preparatory refactoring.

gdb may or may not be affected by this, depending on how it uses the
NT_PRFPREG and NT_ARM_SVE regsets.  I'll leave it to the developers to
assess that.


[1] [PATCH 0/2] arm64/sve: Fix mutating register endianness on big-endian
http://lists.infradead.org/pipermail/linux-arm-kernel/2019-June/657824.html


Dave Martin (3):
  arm64/sve: Fix missing SVE/FPSIMD endianness conversions
  arm64/sve: Factor out FPSIMD to SVE state conversion
  arm64/sve: Fix a couple of magic numbers for the Z-reg count

 Documentation/arm64/sve.txt              | 16 +++++++++++
 arch/arm64/include/uapi/asm/kvm.h        |  7 +++++
 arch/arm64/include/uapi/asm/ptrace.h     |  4 +++
 arch/arm64/include/uapi/asm/sigcontext.h | 14 +++++++++
 arch/arm64/kernel/fpsimd.c               | 49 ++++++++++++++++++++++++--------
 5 files changed, 78 insertions(+), 12 deletions(-)

-- 
2.1.4

[PATCH v2 1/3] arm64/sve: Fix missing SVE/FPSIMD endianness conversions

[Dave Martin]

The in-memory representation of SVE and FPSIMD registers is
different: the FPSIMD V-registers are stored as single 128-bit
host-endian values, whereas SVE registers are stored in an
endianness-invariant byte order.

This means that the two representations differ when running on a
big-endian host.  But we blindly copy data from one representation
to another when converting between the two, resulting in the
register contents being unintentionally byteswapped in certain
situations.  Currently this can be triggered by the first SVE
instruction after a syscall, for example (though the potential
trigger points may vary in future).

So, fix the conversion functions fpsimd_to_sve(), sve_to_fpsimd()
and sve_sync_from_fpsimd_zeropad() to swab where appropriate.

There is no common swahl128() or swab128() that we could use here.
Maybe it would be worth making this generic, but for now add a
simple local hack.

Since the byte order differences are exposed in ABI, also clarify
the docuentation.

Fixes: bc0ee4760364 ("arm64/sve: Core task context handling")
Fixes: 8cd969d28fd2 ("arm64/sve: Signal handling support")
Fixes: 43d4da2c45b2 ("arm64/sve: ptrace and ELF coredump support")
Signed-off-by: Dave Martin <Dave.Martin@arm.com>

---

The ptrace change is theoretically an ABI break, but since the current
behaviour is obviously wrong, I consider this a fix.

Tested on the Arm Fast Model, using:

 * asm code that mixes SVE instructions and syscalls;

 * ptrace interactions that mix the SVE_PT_REGS_FPSIMD and
   SVE_PT_REGS_SVE views of NT_ARM_SVE.

Signal frame behaviour not directly tested (since the underlying
conversion functions are the same in all cases).

Demonstrator code, on a big-endian platform:

.arch_extension sve

	index	z0.b, #0, #1
	str	v0, [x0]
// x0 -> 0f 0e 0d 0c 0b 0a 09 08 07 06 05 04 03 02 01 00

	mov	w8, #__NR_getpid
	svc	#0	// any noop syscall, reverts to non-SVE regs
	str	v0, [x0]
// x0 -> 0f 0e 0d 0c 0b 0a 09 08 07 06 05 04 03 02 01 00

	mov	z0.d, z0.d
	// triggers an SVE trap and buggy FPSIMD->SVE conversion
	str	v0, [x0]
// x0 -> 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f

While a "cool feature", this is not what was intended.
---
 Documentation/arm64/sve.txt              | 16 ++++++++++++
 arch/arm64/include/uapi/asm/kvm.h        |  7 ++++++
 arch/arm64/include/uapi/asm/ptrace.h     |  4 +++
 arch/arm64/include/uapi/asm/sigcontext.h | 14 +++++++++++
 arch/arm64/kernel/fpsimd.c               | 42 +++++++++++++++++++++++++-------
 5 files changed, 74 insertions(+), 9 deletions(-)

diff --git a/Documentation/arm64/sve.txt b/Documentation/arm64/sve.txt
index 9940e92..6c0bed3 100644
--- a/Documentation/arm64/sve.txt
+++ b/Documentation/arm64/sve.txt
@@ -56,6 +56,18 @@ model features for SVE is included in Appendix A.
   is to connect to a target process first and then attempt a
   ptrace(PTRACE_GETREGSET, pid, NT_ARM_SVE, &iov).
 
+* Whenever SVE scalable register values (Zn, Pn, FFR) are exchanged in memory
+  between userspace and the kernel, the register value is encoded in memory in
+  an endianness-invariant layout, with bits [(8 * i + 7) : (8 * i)] encoded at
+  byte offset i in from the start of the memory representation.  This affects
+  for example the signal frame (struct sve_context) and ptrace interface
+  (struct user_sve_header) and associated data.
+
+  Beware that on big-endian systems this results in a different byte order than
+  for the FPSIMD V-registers, which are stored as single host-endian 128-bit
+  values, with bits [(127 - 8 * i) : (120 - 8 * i)] of the register encoded at
+  byte offset i.  (struct fpsimd_context, struct user_fpsimd_state).
+
 
 2.  Vector length terminology
 -----------------------------
@@ -124,6 +136,10 @@ the SVE instruction set architecture.
   size and layout.  Macros SVE_SIG_* are defined [1] to facilitate access to
   the members.
 
+* Each scalable register (Zn, Pn, FFR) is stored in an endianness-invariant
+  layout, with bits [(8 * i + 7) : (8 * i)] stored at byte offset i from the
+  start of the register's representation in memory.
+
 * If the SVE context is too big to fit in sigcontext.__reserved[], then extra
   space is allocated on the stack, an extra_context record is written in
   __reserved[] referencing this space.  sve_context is then written in the
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 7b7ac0f..072ea1e 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -260,6 +260,13 @@ struct kvm_vcpu_events {
 	 KVM_REG_SIZE_U256 |						\
 	 ((i) & (KVM_ARM64_SVE_MAX_SLICES - 1)))
 
+/*
+ * Register values for KVM_REG_ARM64_SVE_ZREG(), KVM_REG_ARM64_SVE_PREG() and
+ * KVM_REG_ARM64_SVE_FFR() and represented in memory in an endianness-
+ * invariant layout which differs from the layout used for the FPSIMD
+ * V-registers on big-endian systems: see sigcontext.h for more explanaion.
+ */
+
 #define KVM_ARM64_SVE_VQ_MIN __SVE_VQ_MIN
 #define KVM_ARM64_SVE_VQ_MAX __SVE_VQ_MAX
 
diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
index d78623a..018bf7d 100644
--- a/arch/arm64/include/uapi/asm/ptrace.h
+++ b/arch/arm64/include/uapi/asm/ptrace.h
@@ -176,6 +176,10 @@ struct user_sve_header {
  *	FPCR	uint32_t			FPCR
  *
  * Additional data might be appended in the future.
+ *
+ * The Z-, P- and FFR registers and represented in memory in an endianness-
+ * invariant layout which differs from the layout used for the FPSIMD
+ * V-registers on big-endian systems: see sigcontext.h for more explanaion.
  */
 
 #define SVE_PT_SVE_ZREG_SIZE(vq)	__SVE_ZREG_SIZE(vq)
diff --git a/arch/arm64/include/uapi/asm/sigcontext.h b/arch/arm64/include/uapi/asm/sigcontext.h
index 5f3c0ce..5231569 100644
--- a/arch/arm64/include/uapi/asm/sigcontext.h
+++ b/arch/arm64/include/uapi/asm/sigcontext.h
@@ -77,6 +77,15 @@ struct fpsimd_context {
 	__uint128_t vregs[32];
 };
 
+/*
+ * Note: similarly to all other integer fields, each V-register is stored in an
+ * endianness-dependent format, with the byte at offset i from the start of the
+ * in-memory representation of the register value containing
+ *
+ *    bits [(7 + 8 * i) : (8 * i)] of the register on little-endian hosts; or
+ *    bits [(127 - 8 * i) : (120 - 8 * i)] on big-endian hosts.
+ */
+
 /* ESR_EL1 context */
 #define ESR_MAGIC	0x45535201
 
@@ -204,6 +213,11 @@ struct sve_context {
  *	FFR	uint16_t[vq]			first-fault status register
  *
  * Additional data might be appended in the future.
+ *
+ * Unlike vregs[] in fpsimd_context, each SVE scalable register (Z-, P- or FFR)
+ * is encoded in memory an endianness-invariant format, with the byte at offset
+ * i from the start of the in-memory representation containing bits
+ * [(7 + 8 * i) : (8 * i)] of the register value.
  */
 
 #define SVE_SIG_ZREG_SIZE(vq)	__SVE_ZREG_SIZE(vq)
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index a38bf74..bb42cd0 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -39,6 +39,7 @@
 #include <linux/slab.h>
 #include <linux/stddef.h>
 #include <linux/sysctl.h>
+#include <linux/swab.h>
 
 #include <asm/esr.h>
 #include <asm/fpsimd.h>
@@ -352,6 +353,23 @@ static int __init sve_sysctl_init(void) { return 0; }
 #define ZREG(sve_state, vq, n) ((char *)(sve_state) +		\
 	(SVE_SIG_ZREG_OFFSET(vq, n) - SVE_SIG_REGS_OFFSET))
 
+#ifdef CONFIG_CPU_BIG_ENDIAN
+static __uint128_t arm64_cpu_to_le128(__uint128_t x)
+{
+	u64 a = swab64(x);
+	u64 b = swab64(x >> 64);
+
+	return ((__uint128_t)a << 64) | b;
+}
+#else
+static __uint128_t arm64_cpu_to_le128(__uint128_t x)
+{
+	return x;
+}
+#endif
+
+#define arm64_le128_to_cpu(x) arm64_cpu_to_le128(x)
+
 /*
  * Transfer the FPSIMD state in task->thread.uw.fpsimd_state to
  * task->thread.sve_state.
@@ -369,14 +387,16 @@ static void fpsimd_to_sve(struct task_struct *task)
 	void *sst = task->thread.sve_state;
 	struct user_fpsimd_state const *fst = &task->thread.uw.fpsimd_state;
 	unsigned int i;
+	__uint128_t *p;
 
 	if (!system_supports_sve())
 		return;
 
 	vq = sve_vq_from_vl(task->thread.sve_vl);
-	for (i = 0; i < 32; ++i)
-		memcpy(ZREG(sst, vq, i), &fst->vregs[i],
-		       sizeof(fst->vregs[i]));
+	for (i = 0; i < 32; ++i) {
+		p = (__uint128_t *)ZREG(sst, vq, i);
+		*p = arm64_cpu_to_le128(fst->vregs[i]);
+	}
 }
 
 /*
@@ -395,14 +415,16 @@ static void sve_to_fpsimd(struct task_struct *task)
 	void const *sst = task->thread.sve_state;
 	struct user_fpsimd_state *fst = &task->thread.uw.fpsimd_state;
 	unsigned int i;
+	__uint128_t const *p;
 
 	if (!system_supports_sve())
 		return;
 
 	vq = sve_vq_from_vl(task->thread.sve_vl);
-	for (i = 0; i < 32; ++i)
-		memcpy(&fst->vregs[i], ZREG(sst, vq, i),
-		       sizeof(fst->vregs[i]));
+	for (i = 0; i < 32; ++i) {
+		p = (__uint128_t const *)ZREG(sst, vq, i);
+		fst->vregs[i] = arm64_le128_to_cpu(*p);
+	}
 }
 
 #ifdef CONFIG_ARM64_SVE
@@ -491,6 +513,7 @@ void sve_sync_from_fpsimd_zeropad(struct task_struct *task)
 	void *sst = task->thread.sve_state;
 	struct user_fpsimd_state const *fst = &task->thread.uw.fpsimd_state;
 	unsigned int i;
+	__uint128_t *p;
 
 	if (!test_tsk_thread_flag(task, TIF_SVE))
 		return;
@@ -499,9 +522,10 @@ void sve_sync_from_fpsimd_zeropad(struct task_struct *task)
 
 	memset(sst, 0, SVE_SIG_REGS_SIZE(vq));
 
-	for (i = 0; i < 32; ++i)
-		memcpy(ZREG(sst, vq, i), &fst->vregs[i],
-		       sizeof(fst->vregs[i]));
+	for (i = 0; i < 32; ++i) {
+		p = (__uint128_t *)ZREG(sst, vq, i);
+		*p = arm64_cpu_to_le128(fst->vregs[i]);
+	}
 }
 
 int sve_set_vector_length(struct task_struct *task,
-- 
2.1.4

[PATCH v2 3/3] arm64/sve: Fix a couple of magic numbers for the Z-reg count

[Dave Martin]

There are some hand-written instances of "32" to express the number
of SVE Z-registers.

Since this code was written a #define was added for this, so
convert trivial instances of this magic number as appropriate.

No functional change.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
---
 arch/arm64/kernel/fpsimd.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index d2f7544..a5702c3 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -376,7 +376,7 @@ static void __fpsimd_to_sve(void *sst, struct user_fpsimd_state const *fst,
 	unsigned int i;
 	__uint128_t *p;
 
-	for (i = 0; i < 32; ++i) {
+	for (i = 0; i < SVE_NUM_ZREGS; ++i) {
 		p = (__uint128_t *)ZREG(sst, vq, i);
 		*p = arm64_cpu_to_le128(fst->vregs[i]);
 	}
@@ -428,7 +428,7 @@ static void sve_to_fpsimd(struct task_struct *task)
 		return;
 
 	vq = sve_vq_from_vl(task->thread.sve_vl);
-	for (i = 0; i < 32; ++i) {
+	for (i = 0; i < SVE_NUM_ZREGS; ++i) {
 		p = (__uint128_t const *)ZREG(sst, vq, i);
 		fst->vregs[i] = arm64_le128_to_cpu(*p);
 	}
-- 
2.1.4

[PATCH v2 2/3] arm64/sve: Factor out FPSIMD to SVE state conversion

[Dave Martin]

Currently we convert from FPSIMD to SVE register state in memory in
two places.

To ease future maintenance, let's consolidate this in one place.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
---
 arch/arm64/kernel/fpsimd.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index bb42cd0..d2f7544 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -370,6 +370,18 @@ static __uint128_t arm64_cpu_to_le128(__uint128_t x)
 
 #define arm64_le128_to_cpu(x) arm64_cpu_to_le128(x)
 
+static void __fpsimd_to_sve(void *sst, struct user_fpsimd_state const *fst,
+			    unsigned int vq)
+{
+	unsigned int i;
+	__uint128_t *p;
+
+	for (i = 0; i < 32; ++i) {
+		p = (__uint128_t *)ZREG(sst, vq, i);
+		*p = arm64_cpu_to_le128(fst->vregs[i]);
+	}
+}
+
 /*
  * Transfer the FPSIMD state in task->thread.uw.fpsimd_state to
  * task->thread.sve_state.
@@ -386,17 +398,12 @@ static void fpsimd_to_sve(struct task_struct *task)
 	unsigned int vq;
 	void *sst = task->thread.sve_state;
 	struct user_fpsimd_state const *fst = &task->thread.uw.fpsimd_state;
-	unsigned int i;
-	__uint128_t *p;
 
 	if (!system_supports_sve())
 		return;
 
 	vq = sve_vq_from_vl(task->thread.sve_vl);
-	for (i = 0; i < 32; ++i) {
-		p = (__uint128_t *)ZREG(sst, vq, i);
-		*p = arm64_cpu_to_le128(fst->vregs[i]);
-	}
+	__fpsimd_to_sve(sst, fst, vq);
 }
 
 /*
@@ -512,8 +519,6 @@ void sve_sync_from_fpsimd_zeropad(struct task_struct *task)
 	unsigned int vq;
 	void *sst = task->thread.sve_state;
 	struct user_fpsimd_state const *fst = &task->thread.uw.fpsimd_state;
-	unsigned int i;
-	__uint128_t *p;
 
 	if (!test_tsk_thread_flag(task, TIF_SVE))
 		return;
@@ -521,11 +526,7 @@ void sve_sync_from_fpsimd_zeropad(struct task_struct *task)
 	vq = sve_vq_from_vl(task->thread.sve_vl);
 
 	memset(sst, 0, SVE_SIG_REGS_SIZE(vq));
-
-	for (i = 0; i < 32; ++i) {
-		p = (__uint128_t *)ZREG(sst, vq, i);
-		*p = arm64_cpu_to_le128(fst->vregs[i]);
-	}
+	__fpsimd_to_sve(sst, fst, vq);
 }
 
 int sve_set_vector_length(struct task_struct *task,
-- 
2.1.4

Re: [PATCH v2 1/3] arm64/sve: Fix missing SVE/FPSIMD endianness conversions

[Will Deacon]

On Wed, Jun 12, 2019 at 05:00:32PM +0100, Dave Martin wrote:
> The in-memory representation of SVE and FPSIMD registers is
> different: the FPSIMD V-registers are stored as single 128-bit
> host-endian values, whereas SVE registers are stored in an
> endianness-invariant byte order.
> 
> This means that the two representations differ when running on a
> big-endian host.  But we blindly copy data from one representation
> to another when converting between the two, resulting in the
> register contents being unintentionally byteswapped in certain
> situations.  Currently this can be triggered by the first SVE
> instruction after a syscall, for example (though the potential
> trigger points may vary in future).
> 
> So, fix the conversion functions fpsimd_to_sve(), sve_to_fpsimd()
> and sve_sync_from_fpsimd_zeropad() to swab where appropriate.
> 
> There is no common swahl128() or swab128() that we could use here.
> Maybe it would be worth making this generic, but for now add a
> simple local hack.
> 
> Since the byte order differences are exposed in ABI, also clarify
> the docuentation.
> 
> Fixes: bc0ee4760364 ("arm64/sve: Core task context handling")
> Fixes: 8cd969d28fd2 ("arm64/sve: Signal handling support")
> Fixes: 43d4da2c45b2 ("arm64/sve: ptrace and ELF coredump support")
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Thanks, Dave. I've picked this one up and pushed it out to our fixes branch
for 5.2. I assume Catalin will take the other two for 5.3. It's probably
worth proposing some generic 128-bit swab functions too, in case there's any
interest (in which case we could drop our local implementation later on).

Cheers,

Will

Re: [PATCH v2 1/3] arm64/sve: Fix missing SVE/FPSIMD endianness conversions

[Julien Grall]

Hi Dave,

On 12/06/2019 17:00, Dave Martin wrote:
> The in-memory representation of SVE and FPSIMD registers is
> different: the FPSIMD V-registers are stored as single 128-bit
> host-endian values, whereas SVE registers are stored in an
> endianness-invariant byte order.
> 
> This means that the two representations differ when running on a
> big-endian host.  But we blindly copy data from one representation
> to another when converting between the two, resulting in the
> register contents being unintentionally byteswapped in certain
> situations.  Currently this can be triggered by the first SVE
> instruction after a syscall, for example (though the potential
> trigger points may vary in future).
> 
> So, fix the conversion functions fpsimd_to_sve(), sve_to_fpsimd()
> and sve_sync_from_fpsimd_zeropad() to swab where appropriate.
> 
> There is no common swahl128() or swab128() that we could use here.
> Maybe it would be worth making this generic, but for now add a
> simple local hack.
> 
> Since the byte order differences are exposed in ABI, also clarify
> the docuentation.

NIT: s/docuentation/documentation/

Although, it is probably too late to fix this one as Will already took the patch.

[...]

> diff --git a/Documentation/arm64/sve.txt b/Documentation/arm64/sve.txt
> index 9940e92..6c0bed3 100644
> --- a/Documentation/arm64/sve.txt
> +++ b/Documentation/arm64/sve.txt
> @@ -56,6 +56,18 @@ model features for SVE is included in Appendix A.
>     is to connect to a target process first and then attempt a
>     ptrace(PTRACE_GETREGSET, pid, NT_ARM_SVE, &iov).
>   
> +* Whenever SVE scalable register values (Zn, Pn, FFR) are exchanged in memory
> +  between userspace and the kernel, the register value is encoded in memory in
> +  an endianness-invariant layout, with bits [(8 * i + 7) : (8 * i)] encoded at
> +  byte offset i in from the start of the memory representation.  This affects
> +  for example the signal frame (struct sve_context) and ptrace interface
> +  (struct user_sve_header) and associated data.
> +
> +  Beware that on big-endian systems this results in a different byte order than
> +  for the FPSIMD V-registers, which are stored as single host-endian 128-bit
> +  values, with bits [(127 - 8 * i) : (120 - 8 * i)] of the register encoded at
> +  byte offset i.  (struct fpsimd_context, struct user_fpsimd_state).
> +
>   
>   2.  Vector length terminology
>   -----------------------------
> @@ -124,6 +136,10 @@ the SVE instruction set architecture.
>     size and layout.  Macros SVE_SIG_* are defined [1] to facilitate access to
>     the members.
>   
> +* Each scalable register (Zn, Pn, FFR) is stored in an endianness-invariant
> +  layout, with bits [(8 * i + 7) : (8 * i)] stored at byte offset i from the
> +  start of the register's representation in memory.
> +
>   * If the SVE context is too big to fit in sigcontext.__reserved[], then extra
>     space is allocated on the stack, an extra_context record is written in
>     __reserved[] referencing this space.  sve_context is then written in the
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index 7b7ac0f..072ea1e 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -260,6 +260,13 @@ struct kvm_vcpu_events {
>   	 KVM_REG_SIZE_U256 |						\
>   	 ((i) & (KVM_ARM64_SVE_MAX_SLICES - 1)))
>   
> +/*
> + * Register values for KVM_REG_ARM64_SVE_ZREG(), KVM_REG_ARM64_SVE_PREG() and
> + * KVM_REG_ARM64_SVE_FFR() and represented in memory in an endianness-

NIT: s/and represented/are represented/ I think.

> + * invariant layout which differs from the layout used for the FPSIMD
> + * V-registers on big-endian systems: see sigcontext.h for more explanaion.

NIT: s/explanaion/explanation/

Cheers,

-- 
Julien Grall

Re: [PATCH v2 1/3] arm64/sve: Fix missing SVE/FPSIMD endianness conversions

[Will Deacon]

On Wed, Jun 12, 2019 at 06:46:04PM +0100, Julien Grall wrote:
> On 12/06/2019 17:00, Dave Martin wrote:
> > The in-memory representation of SVE and FPSIMD registers is
> > different: the FPSIMD V-registers are stored as single 128-bit
> > host-endian values, whereas SVE registers are stored in an
> > endianness-invariant byte order.
> > 
> > This means that the two representations differ when running on a
> > big-endian host.  But we blindly copy data from one representation
> > to another when converting between the two, resulting in the
> > register contents being unintentionally byteswapped in certain
> > situations.  Currently this can be triggered by the first SVE
> > instruction after a syscall, for example (though the potential
> > trigger points may vary in future).
> > 
> > So, fix the conversion functions fpsimd_to_sve(), sve_to_fpsimd()
> > and sve_sync_from_fpsimd_zeropad() to swab where appropriate.
> > 
> > There is no common swahl128() or swab128() that we could use here.
> > Maybe it would be worth making this generic, but for now add a
> > simple local hack.
> > 
> > Since the byte order differences are exposed in ABI, also clarify
> > the docuentation.
> 
> NIT: s/docuentation/documentation/
> 
> Although, it is probably too late to fix this one as Will already took the patch.

I actually spotted (and fixed) that one when I committed the patch, but I
missed the others. Given that this is top of the fixes branch, I can
probably just fold these in.

Will

Re: [PATCH v2 1/3] arm64/sve: Fix missing SVE/FPSIMD endianness conversions

[Dave Martin]

On Wed, Jun 12, 2019 at 06:46:04PM +0100, Julien Grall wrote:
> Hi Dave,
> 
> On 12/06/2019 17:00, Dave Martin wrote:
> >The in-memory representation of SVE and FPSIMD registers is
> >different: the FPSIMD V-registers are stored as single 128-bit
> >host-endian values, whereas SVE registers are stored in an
> >endianness-invariant byte order.
> >
> >This means that the two representations differ when running on a
> >big-endian host.  But we blindly copy data from one representation
> >to another when converting between the two, resulting in the
> >register contents being unintentionally byteswapped in certain
> >situations.  Currently this can be triggered by the first SVE
> >instruction after a syscall, for example (though the potential
> >trigger points may vary in future).
> >
> >So, fix the conversion functions fpsimd_to_sve(), sve_to_fpsimd()
> >and sve_sync_from_fpsimd_zeropad() to swab where appropriate.
> >
> >There is no common swahl128() or swab128() that we could use here.
> >Maybe it would be worth making this generic, but for now add a
> >simple local hack.
> >
> >Since the byte order differences are exposed in ABI, also clarify
> >the docuentation.
> 
> NIT: s/docuentation/documentation/
> 
> Although, it is probably too late to fix this one as Will already took the patch.
> 
> [...]
> 
> >diff --git a/Documentation/arm64/sve.txt b/Documentation/arm64/sve.txt
> >index 9940e92..6c0bed3 100644
> >--- a/Documentation/arm64/sve.txt
> >+++ b/Documentation/arm64/sve.txt
> >@@ -56,6 +56,18 @@ model features for SVE is included in Appendix A.
> >    is to connect to a target process first and then attempt a
> >    ptrace(PTRACE_GETREGSET, pid, NT_ARM_SVE, &iov).
> >+* Whenever SVE scalable register values (Zn, Pn, FFR) are exchanged in memory
> >+  between userspace and the kernel, the register value is encoded in memory in
> >+  an endianness-invariant layout, with bits [(8 * i + 7) : (8 * i)] encoded at
> >+  byte offset i in from the start of the memory representation.  This affects
> >+  for example the signal frame (struct sve_context) and ptrace interface
> >+  (struct user_sve_header) and associated data.
> >+
> >+  Beware that on big-endian systems this results in a different byte order than
> >+  for the FPSIMD V-registers, which are stored as single host-endian 128-bit
> >+  values, with bits [(127 - 8 * i) : (120 - 8 * i)] of the register encoded at
> >+  byte offset i.  (struct fpsimd_context, struct user_fpsimd_state).
> >+
> >  2.  Vector length terminology
> >  -----------------------------
> >@@ -124,6 +136,10 @@ the SVE instruction set architecture.
> >    size and layout.  Macros SVE_SIG_* are defined [1] to facilitate access to
> >    the members.
> >+* Each scalable register (Zn, Pn, FFR) is stored in an endianness-invariant
> >+  layout, with bits [(8 * i + 7) : (8 * i)] stored at byte offset i from the
> >+  start of the register's representation in memory.
> >+
> >  * If the SVE context is too big to fit in sigcontext.__reserved[], then extra
> >    space is allocated on the stack, an extra_context record is written in
> >    __reserved[] referencing this space.  sve_context is then written in the
> >diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> >index 7b7ac0f..072ea1e 100644
> >--- a/arch/arm64/include/uapi/asm/kvm.h
> >+++ b/arch/arm64/include/uapi/asm/kvm.h
> >@@ -260,6 +260,13 @@ struct kvm_vcpu_events {
> >  	 KVM_REG_SIZE_U256 |						\
> >  	 ((i) & (KVM_ARM64_SVE_MAX_SLICES - 1)))
> >+/*
> >+ * Register values for KVM_REG_ARM64_SVE_ZREG(), KVM_REG_ARM64_SVE_PREG() and
> >+ * KVM_REG_ARM64_SVE_FFR() and represented in memory in an endianness-
> 
> NIT: s/and represented/are represented/ I think.
> 
> >+ * invariant layout which differs from the layout used for the FPSIMD
> >+ * V-registers on big-endian systems: see sigcontext.h for more explanaion.
> 
> NIT: s/explanaion/explanation/

Dang, the first of these two is quite confusing.

I might send a fix for that, but I guess it's not urgent.  Thanks for
spotting it.

Cheers
---Dave

Re: [PATCH v2 1/3] arm64/sve: Fix missing SVE/FPSIMD endianness conversions

[Will Deacon]

On Thu, Jun 13, 2019 at 11:00:34AM +0100, Dave Martin wrote:
> On Wed, Jun 12, 2019 at 06:46:04PM +0100, Julien Grall wrote:
> > On 12/06/2019 17:00, Dave Martin wrote:
> > >diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> > >index 7b7ac0f..072ea1e 100644
> > >--- a/arch/arm64/include/uapi/asm/kvm.h
> > >+++ b/arch/arm64/include/uapi/asm/kvm.h
> > >@@ -260,6 +260,13 @@ struct kvm_vcpu_events {
> > >  	 KVM_REG_SIZE_U256 |						\
> > >  	 ((i) & (KVM_ARM64_SVE_MAX_SLICES - 1)))
> > >+/*
> > >+ * Register values for KVM_REG_ARM64_SVE_ZREG(), KVM_REG_ARM64_SVE_PREG() and
> > >+ * KVM_REG_ARM64_SVE_FFR() and represented in memory in an endianness-
> > 
> > NIT: s/and represented/are represented/ I think.
> > 
> > >+ * invariant layout which differs from the layout used for the FPSIMD
> > >+ * V-registers on big-endian systems: see sigcontext.h for more explanaion.
> > 
> > NIT: s/explanaion/explanation/
> 
> Dang, the first of these two is quite confusing.
> 
> I might send a fix for that, but I guess it's not urgent.  Thanks for
> spotting it.

I've pushed an updated version out so hopefully no need to do anything more.

Will

Re: [PATCH v2 1/3] arm64/sve: Fix missing SVE/FPSIMD endianness conversions

[Dave Martin]

On Thu, Jun 13, 2019 at 11:17:27AM +0100, Will Deacon wrote:
> On Thu, Jun 13, 2019 at 11:00:34AM +0100, Dave Martin wrote:
> > On Wed, Jun 12, 2019 at 06:46:04PM +0100, Julien Grall wrote:
> > > On 12/06/2019 17:00, Dave Martin wrote:
> > > >diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> > > >index 7b7ac0f..072ea1e 100644
> > > >--- a/arch/arm64/include/uapi/asm/kvm.h
> > > >+++ b/arch/arm64/include/uapi/asm/kvm.h
> > > >@@ -260,6 +260,13 @@ struct kvm_vcpu_events {
> > > >  	 KVM_REG_SIZE_U256 |						\
> > > >  	 ((i) & (KVM_ARM64_SVE_MAX_SLICES - 1)))
> > > >+/*
> > > >+ * Register values for KVM_REG_ARM64_SVE_ZREG(), KVM_REG_ARM64_SVE_PREG() and
> > > >+ * KVM_REG_ARM64_SVE_FFR() and represented in memory in an endianness-
> > > 
> > > NIT: s/and represented/are represented/ I think.
> > > 
> > > >+ * invariant layout which differs from the layout used for the FPSIMD
> > > >+ * V-registers on big-endian systems: see sigcontext.h for more explanaion.
> > > 
> > > NIT: s/explanaion/explanation/
> > 
> > Dang, the first of these two is quite confusing.
> > 
> > I might send a fix for that, but I guess it's not urgent.  Thanks for
> > spotting it.
> 
> I've pushed an updated version out so hopefully no need to do anything more.

Ah, OK.  Great.

Thanks
---Dave

Re: [PATCH v2 3/3] arm64/sve: Fix a couple of magic numbers for the Z-reg count

[Julien Grall]

Hi Dave,

On 6/12/19 5:00 PM, Dave Martin wrote:
> There are some hand-written instances of "32" to express the number
> of SVE Z-registers.
> 
> Since this code was written a #define was added for this, so
> convert trivial instances of this magic number as appropriate.
> 
> No functional change.
> 
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Julien Grall <julien.grall@arm.com>

Cheers,

-- 
Julien Grall

Re: [PATCH v2 2/3] arm64/sve: Factor out FPSIMD to SVE state conversion

[Julien Grall]

Hi Dave,

On 6/12/19 5:00 PM, Dave Martin wrote:
> Currently we convert from FPSIMD to SVE register state in memory in
> two places.
> 
> To ease future maintenance, let's consolidate this in one place.
> 
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Reviewed-by: Julien Grall <julien.grall@arm.com>

Cheers,

-- 
Julien Grall

Re: [PATCH v2 1/3] arm64/sve: Fix missing SVE/FPSIMD endianness conversions

[Dave Martin]

On Thu, Jun 27, 2019 at 02:51:13PM +0100, Catalin Marinas wrote:
> On Wed, Jun 12, 2019 at 06:28:53PM +0100, Will Deacon wrote:
> > On Wed, Jun 12, 2019 at 05:00:32PM +0100, Dave Martin wrote:
> > > The in-memory representation of SVE and FPSIMD registers is
> > > different: the FPSIMD V-registers are stored as single 128-bit
> > > host-endian values, whereas SVE registers are stored in an
> > > endianness-invariant byte order.
> > > 
> > > This means that the two representations differ when running on a
> > > big-endian host.  But we blindly copy data from one representation
> > > to another when converting between the two, resulting in the
> > > register contents being unintentionally byteswapped in certain
> > > situations.  Currently this can be triggered by the first SVE
> > > instruction after a syscall, for example (though the potential
> > > trigger points may vary in future).
> > > 
> > > So, fix the conversion functions fpsimd_to_sve(), sve_to_fpsimd()
> > > and sve_sync_from_fpsimd_zeropad() to swab where appropriate.
> > > 
> > > There is no common swahl128() or swab128() that we could use here.
> > > Maybe it would be worth making this generic, but for now add a
> > > simple local hack.
> > > 
> > > Since the byte order differences are exposed in ABI, also clarify
> > > the docuentation.
> > > 
> > > Fixes: bc0ee4760364 ("arm64/sve: Core task context handling")
> > > Fixes: 8cd969d28fd2 ("arm64/sve: Signal handling support")
> > > Fixes: 43d4da2c45b2 ("arm64/sve: ptrace and ELF coredump support")
> > > Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> > 
> > Thanks, Dave. I've picked this one up and pushed it out to our fixes branch
> > for 5.2. I assume Catalin will take the other two for 5.3.
> 
> At least the second patch depends on the first one. So I'll postpone
> merging them until -rc1.

Yes, that should be fine.  Those are cleanup, supplementary to the fix.

Thanks
---Dave

Re: [PATCH v2 2/3] arm64/sve: Factor out FPSIMD to SVE state conversion

[Catalin Marinas]

On Wed, Jun 12, 2019 at 05:00:33PM +0100, Dave P Martin wrote:
> Currently we convert from FPSIMD to SVE register state in memory in
> two places.
> 
> To ease future maintenance, let's consolidate this in one place.
> 
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Now that we are at 5.3-rc1 and Will is queuing fixes, he can take this
patch as well (I didn't queue it for the merging window because of a
dependency on the first patch).

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

Re: [PATCH v2 3/3] arm64/sve: Fix a couple of magic numbers for the Z-reg count

[Catalin Marinas]

On Wed, Jun 12, 2019 at 05:00:34PM +0100, Dave P Martin wrote:
> There are some hand-written instances of "32" to express the number
> of SVE Z-registers.
> 
> Since this code was written a #define was added for this, so
> convert trivial instances of this magic number as appropriate.
> 
> No functional change.
> 
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Same here, Will can queue this for -rc2.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>