Re: [PATCH] powerpc: Fix non-atomic stack pointer update in fortified longjmp (bug 34530)

On 17/08/26 10:07, Florian Weimer wrote:
> After commit 78f1f0e39cd41d28ae771eb3498bc33780c85cfd ("Consolidate
> the C pointer guard and align the assembly implementations"),
> PTR_DEMANGLE3 on POWER no longer atomically updates the destination
> register. The fortified longjmp relies on atomic update of the
> stack pointer (r1) in sysdeps/powerpc/powerpc64/__longjmp-common.S
> and parallel files:
> 
> #ifdef PTR_DEMANGLE
> # ifdef CHECK_SP
>         PTR_DEMANGLE3 (r22, r22, r25)
> # else
>         PTR_DEMANGLE3 (r1, r22, r25)
> # endif
> #endif
> 
> Fix this by using PTR_DEMANGLE2 instead of PTR_DEMANGLE3.  Remove
> PTR_MANGLE3 and PTR_DEMANGLE3 as unused.
> 
> An alternate fix would store the pointer guard cookie rotated,
> but this would go against the unification in the commit that
> introduced the regression.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <[email protected]>

> 
> ---
>  sysdeps/powerpc/powerpc32/__longjmp-common.S        | 10 ++++------
>  sysdeps/powerpc/powerpc32/fpu/__longjmp-common.S    | 11 ++++-------
>  sysdeps/powerpc/powerpc64/__longjmp-common.S        | 16 ++++++----------
>  sysdeps/unix/sysv/linux/powerpc/pointer_guard-asm.h |  8 --------
>  4 files changed, 14 insertions(+), 31 deletions(-)
> 
> diff --git a/sysdeps/powerpc/powerpc32/__longjmp-common.S b/sysdeps/powerpc/powerpc32/__longjmp-common.S
> index eb228bf4fe..9da86330f7 100644
> --- a/sysdeps/powerpc/powerpc32/__longjmp-common.S
> +++ b/sysdeps/powerpc/powerpc32/__longjmp-common.S
> @@ -30,11 +30,12 @@ ENTRY (__longjmp_symbol)
>  
>  #if defined PTR_DEMANGLE || defined CHECK_SP
>  	lwz r24,(JB_GPR1*4)(r3)
> +# ifdef PTR_DEMANGLE
> +	PTR_DEMANGLE (r24, r25)
> +# endif
>  # ifdef CHECK_SP
> -#  ifdef PTR_DEMANGLE
> -	PTR_DEMANGLE3 (r24, r24, r25)
> -#  endif
>  	CHECK_SP (r24)
> +# endif
>  	mr r1,r24
>  # endif
>  #else
> @@ -49,9 +50,6 @@ ENTRY (__longjmp_symbol)
>  	lwz r19,((JB_GPRS+19-14)*4)(r3)
>  	lwz r20,((JB_GPRS+20-14)*4)(r3)
>  #ifdef PTR_DEMANGLE
> -# ifndef CHECK_SP
> -	PTR_DEMANGLE3 (r1, r24, r25)
> -# endif
>  	PTR_DEMANGLE2 (r0, r25)
>  #endif
>  	/* longjmp/longjmp_target probe expects longjmp first argument (4@3),
> diff --git a/sysdeps/powerpc/powerpc32/fpu/__longjmp-common.S b/sysdeps/powerpc/powerpc32/fpu/__longjmp-common.S
> index c5acc1610c..8e383cc997 100644
> --- a/sysdeps/powerpc/powerpc32/fpu/__longjmp-common.S
> +++ b/sysdeps/powerpc/powerpc32/fpu/__longjmp-common.S
> @@ -114,13 +114,13 @@ L(no_vmx):
>  #endif
>  #if defined PTR_DEMANGLE || defined CHECK_SP
>  	lwz r24,(JB_GPR1*4)(r3)
> +# ifdef PTR_DEMANGLE
> +	PTR_DEMANGLE (r24, r25)
> +# endif
>  # ifdef CHECK_SP
> -#  ifdef PTR_DEMANGLE
> -	PTR_DEMANGLE3 (r24, r24, r25)
> -#  endif
>  	CHECK_SP (r24)
> +# endif
>  	mr r1,r24
> -# endif
>  #else
>  	lwz r1,(JB_GPR1*4)(r3)
>  #endif
> @@ -140,9 +140,6 @@ L(no_vmx):
>  	lwz r20,((JB_GPRS+6)*4)(r3)
>  	lfd fp20,((JB_FPRS+6*2)*4)(r3)
>  #ifdef PTR_DEMANGLE
> -# ifndef CHECK_SP
> -	PTR_DEMANGLE3 (r1, r24, r25)
> -# endif
>  	PTR_DEMANGLE2 (r0, r25)
>  #endif
>  	/* longjmp/longjmp_target probe expects longjmp first argument (4@3),
> diff --git a/sysdeps/powerpc/powerpc64/__longjmp-common.S b/sysdeps/powerpc/powerpc64/__longjmp-common.S
> index 99b2718677..fe8488fcac 100644
> --- a/sysdeps/powerpc/powerpc64/__longjmp-common.S
> +++ b/sysdeps/powerpc/powerpc64/__longjmp-common.S
> @@ -115,19 +115,15 @@ L(no_vmx):
>  #endif
>  #if defined PTR_DEMANGLE || defined CHECK_SP
>  	ld r22,(JB_GPR1*8)(r3)
> -#else
> -	ld r1,(JB_GPR1*8)(r3)
> -#endif
> -#ifdef PTR_DEMANGLE
> +# ifdef PTR_DEMANGLE
> +	PTR_DEMANGLE (r22, r25)
> +# endif
>  # ifdef CHECK_SP
> -	PTR_DEMANGLE3 (r22, r22, r25)
> -# else
> -	PTR_DEMANGLE3 (r1, r22, r25)
> -# endif
> -#endif
> -#ifdef CHECK_SP
>  	CHECK_SP (r22)
> +# endif
>  	mr r1,r22
> +#else
> +	ld r1,(JB_GPR1*8)(r3)
>  #endif
>  	ld r2,(JB_GPR2*8)(r3)
>  	ld r0,(JB_LR*8)(r3)
> diff --git a/sysdeps/unix/sysv/linux/powerpc/pointer_guard-asm.h b/sysdeps/unix/sysv/linux/powerpc/pointer_guard-asm.h
> index 962ad10e59..cb3e031467 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/pointer_guard-asm.h
> +++ b/sysdeps/unix/sysv/linux/powerpc/pointer_guard-asm.h
> @@ -65,10 +65,6 @@
>  # define PTR_MANGLE2(reg, tmpreg) \
>  	xor	reg,tmpreg,reg; \
>  	PTR_ROT_MANGLE (reg, reg)
> -# define PTR_MANGLE3(destreg, reg, tmpreg) \
> -	PTR_GUARD_LOAD (tmpreg); \
> -	xor	destreg,tmpreg,reg; \
> -	PTR_ROT_MANGLE (destreg, destreg)
>  # define PTR_DEMANGLE(reg, tmpreg) \
>  	PTR_GUARD_LOAD (tmpreg); \
>  	PTR_ROT_DEMANGLE (reg, reg); \
> @@ -76,10 +72,6 @@
>  # define PTR_DEMANGLE2(reg, tmpreg) \
>  	PTR_ROT_DEMANGLE (reg, reg); \
>  	xor	reg,tmpreg,reg
> -# define PTR_DEMANGLE3(destreg, reg, tmpreg) \
> -	PTR_GUARD_LOAD (tmpreg); \
> -	PTR_ROT_DEMANGLE (destreg, reg); \
> -	xor	destreg,tmpreg,destreg
>  #endif
>  
>  #endif /* POINTER_GUARD_ASM_H */
> 
> base-commit: c6ddcef3985e887cf3a469549da2120c2b0e63fb
>