[PATCH v3 1/1] target/ppc: don't byte swap ELFv2 signal handler

[PATCH v3 1/1] target/ppc: don't byte swap ELFv2 signal handler

[Vincent Fazio]

From: Vincent Fazio <vfazio@gmail.com>

Previously, the signal handler would be byte swapped if the target and
host CPU used different endianness. This would cause a SIGSEGV when
attempting to translate the opcode pointed to by the swapped address.

 Thread 1 "qemu-ppc64" received signal SIGSEGV, Segmentation fault.
 0x00000000600a9257 in ldl_he_p (ptr=0x4c2c061000000000) at qemu/include/qemu/bswap.h:351
 351        __builtin_memcpy(&r, ptr, sizeof(r));

 #0  0x00000000600a9257 in ldl_he_p (ptr=0x4c2c061000000000) at qemu/include/qemu/bswap.h:351
 #1  0x00000000600a92fe in ldl_be_p (ptr=0x4c2c061000000000) at qemu/include/qemu/bswap.h:449
 #2  0x00000000600c0790 in translator_ldl_swap at qemu/include/exec/translator.h:201
 #3  0x000000006011c1ab in ppc_tr_translate_insn at qemu/target/ppc/translate.c:7856
 #4  0x000000006005ae70 in translator_loop at qemu/accel/tcg/translator.c:102

The signal handler will be byte swapped as a result of the __get_user()
call in sigaction() if it is necessary, no additional swap is required.

Signed-off-by: Vincent Fazio <vfazio@gmail.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
---
Changes since v2:
- Explain why the swap is not necessary

Changes since v1:
- Drop host/target endianness callouts
- Drop unnecessary pointer cast
- Clarify commit message

 linux-user/ppc/signal.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/linux-user/ppc/signal.c b/linux-user/ppc/signal.c
index 5b82af6cb6..b8613c5e1b 100644
--- a/linux-user/ppc/signal.c
+++ b/linux-user/ppc/signal.c
@@ -567,10 +567,8 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
         env->nip = tswapl(handler->entry);
         env->gpr[2] = tswapl(handler->toc);
     } else {
-        /* ELFv2 PPC64 function pointers are entry points, but R12
-         * must also be set */
-        env->nip = tswapl((target_ulong) ka->_sa_handler);
-        env->gpr[12] = env->nip;
+        /* ELFv2 PPC64 function pointers are entry points. R12 must also be set. */
+        env->gpr[12] = env->nip = ka->_sa_handler;
     }
 #else
     env->nip = (target_ulong) ka->_sa_handler;
-- 
2.25.1

Re: [PATCH v3 1/1] target/ppc: don't byte swap ELFv2 signal handler

[David Gibson]

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On Thu, Mar 19, 2020 at 08:32:44AM -0500, Vincent Fazio wrote:
> From: Vincent Fazio <vfazio@gmail.com>
> 
> Previously, the signal handler would be byte swapped if the target and
> host CPU used different endianness. This would cause a SIGSEGV when
> attempting to translate the opcode pointed to by the swapped address.
> 
>  Thread 1 "qemu-ppc64" received signal SIGSEGV, Segmentation fault.
>  0x00000000600a9257 in ldl_he_p (ptr=0x4c2c061000000000) at qemu/include/qemu/bswap.h:351
>  351        __builtin_memcpy(&r, ptr, sizeof(r));
> 
>  #0  0x00000000600a9257 in ldl_he_p (ptr=0x4c2c061000000000) at qemu/include/qemu/bswap.h:351
>  #1  0x00000000600a92fe in ldl_be_p (ptr=0x4c2c061000000000) at qemu/include/qemu/bswap.h:449
>  #2  0x00000000600c0790 in translator_ldl_swap at qemu/include/exec/translator.h:201
>  #3  0x000000006011c1ab in ppc_tr_translate_insn at qemu/target/ppc/translate.c:7856
>  #4  0x000000006005ae70 in translator_loop at qemu/accel/tcg/translator.c:102
> 
> The signal handler will be byte swapped as a result of the __get_user()
> call in sigaction() if it is necessary, no additional swap is required.
> 
> Signed-off-by: Vincent Fazio <vfazio@gmail.com>
> Reviewed-by: Laurent Vivier <laurent@vivier.eu>
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

Applied to ppc-for-5.0, thanks.

> ---
> Changes since v2:
> - Explain why the swap is not necessary
> 
> Changes since v1:
> - Drop host/target endianness callouts
> - Drop unnecessary pointer cast
> - Clarify commit message
> 
>  linux-user/ppc/signal.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/linux-user/ppc/signal.c b/linux-user/ppc/signal.c
> index 5b82af6cb6..b8613c5e1b 100644
> --- a/linux-user/ppc/signal.c
> +++ b/linux-user/ppc/signal.c
> @@ -567,10 +567,8 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
>          env->nip = tswapl(handler->entry);
>          env->gpr[2] = tswapl(handler->toc);
>      } else {
> -        /* ELFv2 PPC64 function pointers are entry points, but R12
> -         * must also be set */
> -        env->nip = tswapl((target_ulong) ka->_sa_handler);
> -        env->gpr[12] = env->nip;
> +        /* ELFv2 PPC64 function pointers are entry points. R12 must also be set. */
> +        env->gpr[12] = env->nip = ka->_sa_handler;
>      }
>  #else
>      env->nip = (target_ulong) ka->_sa_handler;

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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