Re: [PATCH v6 1/3] x86_64: Set the syscall register right before doing the syscall.

[Joe Simmons-Talbott <josimmon@redhat.com>]

ping.

Thanks,
Joe
On Mon, Apr 24, 2023 at 11:03:51AM -0400, Joe Simmons-Talbott wrote:
> To make identifying syscalls easier during call tree analysis load the
> syscall number just before performing the syscall.
> 
> Compiler optimizations can place quite a few instructions between the
> setting of the syscall number and the syscall instruction.  During call
> tree analysis the number of instructions between the two can lead to
> more difficulty for both tools and humans in properly identifying the
> syscall number.  Having the syscall number set in the prior instruction
> to the syscall instruction makes this task easier and less error prone.
> Being able to reliably identify syscalls made by a given API will make
> it easier to understand and verify the safety and security of glibc.
> ---
>  sysdeps/unix/sysv/linux/x86_64/sysdep.h | 24 ++++++++++++------------
>  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/x86_64/sysdep.h b/sysdeps/unix/sysv/linux/x86_64/sysdep.h
> index cfb51be8c5..0db8660531 100644
> --- a/sysdeps/unix/sysv/linux/x86_64/sysdep.h
> +++ b/sysdeps/unix/sysv/linux/x86_64/sysdep.h
> @@ -257,9 +257,9 @@
>      TYPEFY (arg1, __arg1) = ARGIFY (arg1);			 	\
>      register TYPEFY (arg1, _a1) asm ("rdi") = __arg1;			\
>      asm volatile (							\
> -    "syscall\n\t"							\
> +    "movl %1, %k0\n\tsyscall\n\t"					\
>      : "=a" (resultvar)							\
> -    : "0" (number), "r" (_a1)						\
> +    : "g" (number), "r" (_a1)						\
>      : "memory", REGISTERS_CLOBBERED_BY_SYSCALL);			\
>      (long int) resultvar;						\
>  })
> @@ -273,9 +273,9 @@
>      register TYPEFY (arg2, _a2) asm ("rsi") = __arg2;			\
>      register TYPEFY (arg1, _a1) asm ("rdi") = __arg1;			\
>      asm volatile (							\
> -    "syscall\n\t"							\
> +    "movl %1, %k0\n\tsyscall\n\t"					\
>      : "=a" (resultvar)							\
> -    : "0" (number), "r" (_a1), "r" (_a2)				\
> +    : "g" (number), "r" (_a1), "r" (_a2)				\
>      : "memory", REGISTERS_CLOBBERED_BY_SYSCALL);			\
>      (long int) resultvar;						\
>  })
> @@ -291,9 +291,9 @@
>      register TYPEFY (arg2, _a2) asm ("rsi") = __arg2;			\
>      register TYPEFY (arg1, _a1) asm ("rdi") = __arg1;			\
>      asm volatile (							\
> -    "syscall\n\t"							\
> +    "movl %1, %k0\n\tsyscall\n\t"					\
>      : "=a" (resultvar)							\
> -    : "0" (number), "r" (_a1), "r" (_a2), "r" (_a3)			\
> +    : "g" (number), "r" (_a1), "r" (_a2), "r" (_a3)			\
>      : "memory", REGISTERS_CLOBBERED_BY_SYSCALL);			\
>      (long int) resultvar;						\
>  })
> @@ -311,9 +311,9 @@
>      register TYPEFY (arg2, _a2) asm ("rsi") = __arg2;			\
>      register TYPEFY (arg1, _a1) asm ("rdi") = __arg1;			\
>      asm volatile (							\
> -    "syscall\n\t"							\
> +    "movl %1, %k0\n\tsyscall\n\t"					\
>      : "=a" (resultvar)							\
> -    : "0" (number), "r" (_a1), "r" (_a2), "r" (_a3), "r" (_a4)		\
> +    : "g" (number), "r" (_a1), "r" (_a2), "r" (_a3), "r" (_a4)		\
>      : "memory", REGISTERS_CLOBBERED_BY_SYSCALL);			\
>      (long int) resultvar;						\
>  })
> @@ -333,9 +333,9 @@
>      register TYPEFY (arg2, _a2) asm ("rsi") = __arg2;			\
>      register TYPEFY (arg1, _a1) asm ("rdi") = __arg1;			\
>      asm volatile (							\
> -    "syscall\n\t"							\
> +    "movl %1, %k0\n\tsyscall\n\t"					\
>      : "=a" (resultvar)							\
> -    : "0" (number), "r" (_a1), "r" (_a2), "r" (_a3), "r" (_a4),		\
> +    : "g" (number), "r" (_a1), "r" (_a2), "r" (_a3), "r" (_a4),		\
>        "r" (_a5)								\
>      : "memory", REGISTERS_CLOBBERED_BY_SYSCALL);			\
>      (long int) resultvar;						\
> @@ -358,9 +358,9 @@
>      register TYPEFY (arg2, _a2) asm ("rsi") = __arg2;			\
>      register TYPEFY (arg1, _a1) asm ("rdi") = __arg1;			\
>      asm volatile (							\
> -    "syscall\n\t"							\
> +    "movl %1, %k0\n\tsyscall\n\t"					\
>      : "=a" (resultvar)							\
> -    : "0" (number), "r" (_a1), "r" (_a2), "r" (_a3), "r" (_a4),		\
> +    : "g" (number), "r" (_a1), "r" (_a2), "r" (_a3), "r" (_a4),		\
>        "r" (_a5), "r" (_a6)						\
>      : "memory", REGISTERS_CLOBBERED_BY_SYSCALL);			\
>      (long int) resultvar;						\
> -- 
> 2.39.2
>