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>

diff --git a/arch/mips/kernel/scall32-o32.S b/arch/mips/kernel/scall32-o32.S
index 1d39beaf57bd9c6de65a5cc66b3d86b11c729d3e..532a3302ec889dd3ca1e70580c559fe019acfc2f 100644 (file)
--- a/arch/mips/kernel/scall32-o32.S
+++ b/arch/mips/kernel/scall32-o32.S
@@ -192,6 +192,7 @@ 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 a56175b74bf7f4db773459eacb47083cef7e8744..6651759edde0fa7bf5936e19e5d14bfa2bf8df17 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