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

[Philippe Mathieu-Daudé]

On 23/2/23 22:58, Ilya Leoshkevich wrote:
> 32-bit guests may enforce only 4-byte alignment for target_rlimit64,
> whereas 64-bit hosts normally require the 8-byte one. Therefore
> accessing this struct directly is UB.
>
> Fix by adding a local copy.

Shouldn't we fix that globally in __get_user/__put_user?

> 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/syscall.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index a6c426d73cf..8ae7696d8f1 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -12876,7 +12876,7 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int 
> num, abi_long arg1,
>       case TARGET_NR_prlimit64:
>       {
>           /* args: pid, resource number, ptr to new rlimit, ptr to old rlimit */
> -        struct target_rlimit64 *target_rnew, *target_rold;
> +        struct target_rlimit64 *target_rnew, *target_rold, tmp;
>           struct host_rlimit64 rnew, rold, *rnewp = 0;
>           int resource = target_to_host_resource(arg2);
>   
> @@ -12886,8 +12886,9 @@ 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);
> +            memcpy(&tmp, target_rnew, sizeof(tmp));
> +            rnew.rlim_cur = tswap64(tmp.rlim_cur);
> +            rnew.rlim_max = tswap64(tmp.rlim_max);
>               unlock_user_struct(target_rnew, arg3, 0);
>               rnewp = &rnew;
>           }
> @@ -12897,8 +12898,9 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int 
> num, abi_long arg1,
>               if (!lock_user_struct(VERIFY_WRITE, target_rold, arg4, 1)) {
>                   return -TARGET_EFAULT;
>               }
> -            target_rold->rlim_cur = tswap64(rold.rlim_cur);
> -            target_rold->rlim_max = tswap64(rold.rlim_max);
> +            tmp.rlim_cur = tswap64(rold.rlim_cur);
> +            tmp.rlim_max = tswap64(rold.rlim_max);
> +            memcpy(target_rold, &tmp, sizeof(*target_rold));
>               unlock_user_struct(target_rold, arg4, 1);
>           }
>           return ret;