Words are stored in big endian in the guest memory for armeb.

Commit 7f4f0d9ea870 ("linux-user/arm: Implement __kernel_cmpxchg with
host atomics") switched to use qatomic_cmpxchg() to swap a word with the
memory content, but missed to endianess-swap the oldval and newval
values when emulating an armeb CPU.

The bug can be verified with qemu >= v7.2 on any little-endian host,
when starting the armeb binary of the upx program, which just hangs
without this patch.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: qemu-stable@nongnu.org
Reported-by: "Markus F.X.J. Oberhumer" <markus@oberhumer.com>
Reported-by: John Reiser <jreiser@BitWagon.com>
Closes: https://github.com/upx/upx/issues/687

diff --git a/linux-user/arm/cpu_loop.c b/linux-user/arm/cpu_loop.c
index a992423257..ff0bff7c63 100644
--- a/linux-user/arm/cpu_loop.c
+++ b/linux-user/arm/cpu_loop.c
@@ -117,8 +117,8 @@ static void arm_kernel_cmpxchg32_helper(CPUARMState *env)
 {
     uint32_t oldval, newval, val, addr, cpsr, *host_addr;

-    oldval = env->regs[0];
-    newval = env->regs[1];
+    oldval = tswap32(env->regs[0]);
+    newval = tswap32(env->regs[1]);
     addr = env->regs[2];

     mmap_lock();

On 27/7/23 23:19, Helge Deller wrote:
> Words are stored in big endian in the guest memory for armeb.
> 
> Commit 7f4f0d9ea870 ("linux-user/arm: Implement __kernel_cmpxchg with
> host atomics") switched to use qatomic_cmpxchg() to swap a word with the
> memory content, but missed to endianess-swap the oldval and newval
> values when emulating an armeb CPU.
> 
> The bug can be verified with qemu >= v7.2 on any little-endian host,
> when starting the armeb binary of the upx program, which just hangs
> without this patch.
> 
> Signed-off-by: Helge Deller <deller@gmx.de>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Cc: qemu-stable@nongnu.org
> Reported-by: "Markus F.X.J. Oberhumer" <markus@oberhumer.com>
> Reported-by: John Reiser <jreiser@BitWagon.com>
> Closes: https://github.com/upx/upx/issues/687

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

31.07.2023 12:26, Philippe Mathieu-Daudé wrote:
> On 27/7/23 23:19, Helge Deller wrote:
>> Words are stored in big endian in the guest memory for armeb.
..
> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

There was a v3 of this patch already, fwiw.

/mjt

On 7/27/23 14:19, Helge Deller wrote:
> Words are stored in big endian in the guest memory for armeb.
> 
> Commit 7f4f0d9ea870 ("linux-user/arm: Implement __kernel_cmpxchg with
> host atomics") switched to use qatomic_cmpxchg() to swap a word with the
> memory content, but missed to endianess-swap the oldval and newval
> values when emulating an armeb CPU.
> 
> The bug can be verified with qemu >= v7.2 on any little-endian host,
> when starting the armeb binary of the upx program, which just hangs
> without this patch.
> 
> Signed-off-by: Helge Deller <deller@gmx.de>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Cc: qemu-stable@nongnu.org
> Reported-by: "Markus F.X.J. Oberhumer" <markus@oberhumer.com>
> Reported-by: John Reiser <jreiser@BitWagon.com>
> Closes: https://github.com/upx/upx/issues/687
> 
> diff --git a/linux-user/arm/cpu_loop.c b/linux-user/arm/cpu_loop.c
> index a992423257..ff0bff7c63 100644
> --- a/linux-user/arm/cpu_loop.c
> +++ b/linux-user/arm/cpu_loop.c
> @@ -117,8 +117,8 @@ static void arm_kernel_cmpxchg32_helper(CPUARMState *env)
>   {
>       uint32_t oldval, newval, val, addr, cpsr, *host_addr;
> 
> -    oldval = env->regs[0];
> -    newval = env->regs[1];
> +    oldval = tswap32(env->regs[0]);
> +    newval = tswap32(env->regs[1]);
>       addr = env->regs[2];

There's a similar bug with arm_kernel_cmpxchg64_helper just below, but

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

as far as this goes.


r~