Re: [PATCH 1/2] x86: lib: setjmp: fix stack alignment

[Sascha Hauer <sha@pengutronix.de>]

On Mon, Oct 09, 2023 at 01:50:50PM +0200, Ahmad Fatoum wrote:
> x86 stack is expected to be 16-byte aligned to allow for instructions
> like movaps that involve xmm operands to directly use the stack.
> 
> However the 16-byte alignment is what's expected at startup time.
> All later functions will have the stack misaligned by a pointer size's
> worth because call pushes the return address to the call stack.
> 
> Add the missing (mis)alignment. This fixes a segmentation fault observed
> using initjmp on x86_64.
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
>  arch/x86/lib/setjmp_32.S | 4 +++-
>  arch/x86/lib/setjmp_64.S | 2 ++
>  2 files changed, 5 insertions(+), 1 deletion(-)

Applied, thanks

Sascha

> 
> diff --git a/arch/x86/lib/setjmp_32.S b/arch/x86/lib/setjmp_32.S
> index 38dcb68c1b59..30db5f989af6 100644
> --- a/arch/x86/lib/setjmp_32.S
> +++ b/arch/x86/lib/setjmp_32.S
> @@ -8,6 +8,7 @@
>  #define _REGPARM
>  
>  #include <linux/linkage.h>
> +#include <asm-generic/pointer.h>
>  
>  .text
>  .align 8
> @@ -53,7 +54,8 @@ ENDPROC(longjmp)
>  ENTRY(initjmp)
>  
>  	movl %edx, 20(%eax)	/* Return address */
> -	movl %ecx, 4(%eax)	/* Post-return %esp! */
> +	sub $ASM_SZPTR, %ecx	/* ESP - 4 has to be 16-byte aligned on entry */
> +	movl %ecx, 4(%eax)	/* Stack top */
>  	xorl %eax, %eax		/* Return value */
>  	ret
>  
> diff --git a/arch/x86/lib/setjmp_64.S b/arch/x86/lib/setjmp_64.S
> index 28ea576cd22e..d5cf99a1557f 100644
> --- a/arch/x86/lib/setjmp_64.S
> +++ b/arch/x86/lib/setjmp_64.S
> @@ -6,6 +6,7 @@
>   */
>  
>  #include <linux/linkage.h>
> +#include <asm-generic/pointer.h>
>  
>  .text
>  .align 8
> @@ -53,6 +54,7 @@ ENDPROC(longjmp)
>  ENTRY(initjmp)
>  
>  	movq	%rsi, (%rdi)	/* Return address */
> +	sub	$ASM_SZPTR, %rdx	/* RSP - 8 has to be 16-byte aligned on entry */
>  	movq	%rdx, 8(%rdi)	/* Stack top */
>  	xorq	%rax, %rax
>  	ret
> -- 
> 2.39.2
> 
> 
> 

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