> On 12 Oct 2020, at 14:44, Jessica Clarke <jrtc27@xxxxxxxxxx> wrote:
>
> POSIX specifies that the first field of the supplied msgp, namely mtype,
> is a long, not a __kernel_long_t, and it's a user-defined struct due to
> the variable-length mtext field so we can't even bend the spec and make
> it a __kernel_long_t even if we wanted to. Thus we must use the compat
> syscalls on x32 to avoid buffer overreads and overflows in msgsnd and
> msgrcv respectively.
>
> Due to erroneously including the first 4 bytes of mtext in the mtype
> this would previously also cause non-zero msgtyp arguments for msgrcv to
> search for the wrong messages, and if sharing message queues between x32
> and non-x32 (i386 or x86_64) processes this would previously cause mtext
> to "move" and, depending on the direction and ABI combination, lose the
> first 4 bytes.
>
> Signed-off-by: Jessica Clarke <jrtc27@xxxxxxxxxx>
> ---
Ping?
Jess
>
> I have verified that the test at the end of [1] now gives the correct
> result on x32 ("PAYL" not "PAY" as I erroneously claimed it should be in
> the above email) and that both i386 and amd64 give the same output with
> that test as before.
>
> [1] <1156938F-A9A3-4EE9-B059-2294A0B9FBFE@xxxxxxxxxx>
>
> Changes since v1:
> * Uses the same syscall numbers for x32 as amd64 and the current x32
> rather than (further) breaking ABI by allocating new ones from the
> legacy x32 range
>
> arch/x86/entry/syscalls/syscall_64.tbl | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> index f30d6ae9a..f462123f3 100644
> --- a/arch/x86/entry/syscalls/syscall_64.tbl
> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> @@ -77,8 +77,10 @@
> 66 common semctl sys_semctl
> 67 common shmdt sys_shmdt
> 68 common msgget sys_msgget
> -69 common msgsnd sys_msgsnd
> -70 common msgrcv sys_msgrcv
> +69 64 msgsnd sys_msgsnd
> +69 x32 msgsnd compat_sys_msgsnd
> +70 64 msgrcv sys_msgrcv
> +70 x32 msgrcv compat_sys_msgrcv
> 71 common msgctl sys_msgctl
> 72 common fcntl sys_fcntl
> 73 common flock sys_flock
> --
> 2.28.0
>
