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

[Richard Henderson]

On 2/23/23 11:58, 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.
>
> 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;

The bug is that target_rlimit64 uses uint64_t (64-bit host alignment), when it should be 
using abi_ullong (64-bit target alignment).  There are quite a number of these sorts of 
bugs in linux-user.


r~