Re: [PATCH v2 1/2] linux-user: Fix unaligned memory access in prlimit64 syscall

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 24/2/23 00:11, Ilya Leoshkevich wrote:
> target_rlimit64 contains uint64_t fields, so it's 8-byte aligned on
> some hosts, while some guests may align their respective type on a
> 4-byte boundary. This may lead to an unaligned access, which is an UB.
> 
> Fix by defining the fields as abi_ullong. This makes the host alignment
> match that of the guest, and lets the compiler know that it should emit
> code that can deal with the guest alignment.
> 
> While at it, also use __get_user() and __put_user() instead of
> tswap64().
> 
> Fixes: 163a05a8398b ("linux-user: Implement prlimit64 syscall")
> Reported-by: Richard Henderson <richard.henderson@linaro.org>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>   linux-user/generic/target_resource.h | 4 ++--
>   linux-user/syscall.c                 | 8 ++++----
>   2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/linux-user/generic/target_resource.h b/linux-user/generic/target_resource.h
> index 539d8c46772..37d3eb09b3b 100644
> --- a/linux-user/generic/target_resource.h
> +++ b/linux-user/generic/target_resource.h
> @@ -12,8 +12,8 @@ struct target_rlimit {
>   };
>   
>   struct target_rlimit64 {
> -    uint64_t rlim_cur;
> -    uint64_t rlim_max;
> +    abi_ullong rlim_cur;
> +    abi_ullong rlim_max;
>   };
>   
>   #define TARGET_RLIM_INFINITY    ((abi_ulong)-1)
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index a6c426d73cf..1f7a272799b 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -12886,8 +12886,8 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
>               if (!lock_user_struct(VERIFY_READ, target_rnew, arg3, 1)) {
>                   return -TARGET_EFAULT;
>               }
> -            rnew.rlim_cur = tswap64(target_rnew->rlim_cur);
> -            rnew.rlim_max = tswap64(target_rnew->rlim_max);
> +            __get_user(rnew.rlim_cur, &target_rnew->rlim_cur);
> +            __get_user(rnew.rlim_max, &target_rnew->rlim_max);

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