MIPS: Fix restart of indirect syscalls

commit e967ef022e00bb7c2e5b1a42007abfdd52055050 upstream.

When 32-bit MIPS userspace invokes a syscall indirectly via syscall(number,
arg1, ..., arg7), the kernel looks up the actual syscall based on the given
number, shifts the other arguments to the left, and jumps to the syscall.

If the syscall is interrupted by a signal and indicates it needs to be
restarted by the kernel (by returning ERESTARTNOINTR for example), the
syscall must be called directly, since the number is no longer the first
argument, and the other arguments are now staged for a direct call.

Before shifting the arguments, store the syscall number in pt_regs->regs[2].
This gets copied temporarily into pt_regs->regs[0] after the syscall returns.
If the syscall needs to be restarted, handle_signal()/do_signal() copies the
number back to pt_regs->reg[2], which ends up in $v0 once control returns to
userspace.

Signed-off-by: Ed Swierk <eswierk@skyportsystems.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8929/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit 08f865bba9c705aef95268a33393698e5385587e)
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/arch/mips/kernel/scall32-o32.S b/arch/mips/kernel/scall32-o32.S
index b72c55484840867501fea907d04a74e5bad02bc6..44194c1626370d923af31431447a959207f638eb 100644 (file)
--- a/arch/mips/kernel/scall32-o32.S
+++ b/arch/mips/kernel/scall32-o32.S
@@ -194,6 +194,7 @@ illegal_syscall:
        sll     t1, t0, 3
        beqz    v0, einval
        lw      t2, sys_call_table(t1)          # syscall routine
+       sw      a0, PT_R2(sp)                   # call routine directly on restart
 
        /* Some syscalls like execve get their arguments from struct pt_regs
           and claim zero arguments in the syscall table. Thus we have to

diff --git a/arch/mips/kernel/scall64-o32.S b/arch/mips/kernel/scall64-o32.S
index 33ed571ae78af8a7493a2556604be14937aa4643..1f7c01f6a12535d9d3c37ae8685f2c3409134771 100644 (file)
--- a/arch/mips/kernel/scall64-o32.S
+++ b/arch/mips/kernel/scall64-o32.S
@@ -180,6 +180,7 @@ LEAF(sys32_syscall)
        dsll    t1, t0, 3
        beqz    v0, einval
        ld      t2, sys_call_table(t1)          # syscall routine
+       sd      a0, PT_R2(sp)           # call routine directly on restart
 
        move    a0, a1                  # shift argument registers
        move    a1, a2