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    Subject[PATCH 4.9 04/41] MIPS: scall64-o32: Fix indirect syscall number load
    Date
    From: Aurelien Jarno <aurelien@aurel32.net>

    commit 79b4a9cf0e2ea8203ce777c8d5cfa86c71eae86e upstream.

    Commit 4c21b8fd8f14 (MIPS: seccomp: Handle indirect system calls (o32))
    added indirect syscall detection for O32 processes running on MIPS64,
    but it did not work correctly for big endian kernel/processes. The
    reason is that the syscall number is loaded from ARG1 using the lw
    instruction while this is a 64-bit value, so zero is loaded instead of
    the syscall number.

    Fix the code by using the ld instruction instead. When running a 32-bit
    processes on a 64 bit CPU, the values are properly sign-extended, so it
    ensures the value passed to syscall_trace_enter is correct.

    Recent systemd versions with seccomp enabled whitelist the getpid
    syscall for their internal processes (e.g. systemd-journald), but call
    it through syscall(SYS_getpid). This fix therefore allows O32 big endian
    systems with a 64-bit kernel to run recent systemd versions.

    Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
    Cc: <stable@vger.kernel.org> # v3.15+
    Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
    Signed-off-by: Paul Burton <paul.burton@mips.com>
    Cc: Ralf Baechle <ralf@linux-mips.org>
    Cc: James Hogan <jhogan@kernel.org>
    Cc: linux-mips@vger.kernel.org
    Cc: linux-kernel@vger.kernel.org
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/mips/kernel/scall64-o32.S | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/mips/kernel/scall64-o32.S
    +++ b/arch/mips/kernel/scall64-o32.S
    @@ -125,7 +125,7 @@ trace_a_syscall:
    subu t1, v0, __NR_O32_Linux
    move a1, v0
    bnez t1, 1f /* __NR_syscall at offset 0 */
    - lw a1, PT_R4(sp) /* Arg1 for __NR_syscall case */
    + ld a1, PT_R4(sp) /* Arg1 for __NR_syscall case */
    .set pop

    1: jal syscall_trace_enter

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