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* [glibc/arm/gcs] aarch64: Add GCS support to longjmp
@ 2024-02-14 15:06 Szabolcs Nagy
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From: Szabolcs Nagy @ 2024-02-14 15:06 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c3274a8582b4915efea5a16558e730d362bea177
commit c3274a8582b4915efea5a16558e730d362bea177
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date: Thu Feb 23 08:54:04 2023 +0000
aarch64: Add GCS support to longjmp
This implementations ensures that longjmp across different stacks
works: it scans for GCS cap token and switches GCS if necessary
then the target GCSPR is restored with a GCSPOPM loop once the
current GCSPR is on the same GCS.
This makes longjmp linear time in the number of jumped over stack
frames when GCS is enabled.
Diff:
---
sysdeps/aarch64/__longjmp.S | 31 +++++++++++++++++++++++++++++++
sysdeps/aarch64/setjmp.S | 10 ++++++++++
2 files changed, 41 insertions(+)
diff --git a/sysdeps/aarch64/__longjmp.S b/sysdeps/aarch64/__longjmp.S
index 7b6add751e..ecd272262d 100644
--- a/sysdeps/aarch64/__longjmp.S
+++ b/sysdeps/aarch64/__longjmp.S
@@ -91,6 +91,37 @@ ENTRY (__longjmp)
ldp d12, d13, [x0, #JB_D12<<3]
ldp d14, d15, [x0, #JB_D14<<3]
+ /* GCS support. */
+ mov x16, 1
+ CHKFEAT_X16
+ tbnz x16, 0, L(gcs_done)
+ MRS_GCSPR (x2)
+ ldr x3, [x0, #JB_GCSPR]
+ mov x4, x3
+ /* x2: GCSPR now. x3, x4: target GCSPR. x5, x6: tmp regs. */
+L(gcs_scan):
+ cmp x2, x4
+ b.eq L(gcs_pop)
+ sub x4, x4, 8
+ /* Check for a cap token. */
+ ldr x5, [x4]
+ and x6, x4, 0xfffffffffffff000
+ orr x6, x6, 1
+ cmp x5, x6
+ b.eq L(gcs_switch)
+ b L(gcs_scan)
+L(gcs_switch):
+ add x2, x4, 8
+ GCSSS1 (x4)
+ GCSSS2 (xzr)
+L(gcs_pop):
+ cmp x2, x3
+ b.eq L(gcs_done)
+ GCSPOPM (xzr)
+ add x2, x2, 8
+ b L(gcs_pop)
+L(gcs_done):
+
/* Originally this was implemented with a series of
.cfi_restore() directives.
diff --git a/sysdeps/aarch64/setjmp.S b/sysdeps/aarch64/setjmp.S
index 43fdb1b2fb..f7ffccfaba 100644
--- a/sysdeps/aarch64/setjmp.S
+++ b/sysdeps/aarch64/setjmp.S
@@ -57,6 +57,16 @@ ENTRY (__sigsetjmp)
stp d10, d11, [x0, #JB_D10<<3]
stp d12, d13, [x0, #JB_D12<<3]
stp d14, d15, [x0, #JB_D14<<3]
+
+ /* GCS support. */
+ mov x16, 1
+ CHKFEAT_X16
+ tbnz x16, 0, L(gcs_done)
+ MRS_GCSPR (x2)
+ add x2, x2, 8 /* GCS state right after setjmp returns. */
+ str x2, [x0, #JB_GCSPR]
+L(gcs_done):
+
#ifdef PTR_MANGLE
mov x4, sp
PTR_MANGLE (5, 4, 3, 2)
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