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MIPS: Remove pt_regs adjustments in indirect syscall handler 

If a restartable syscall is called using the indirect o32 syscall
handler - eg: syscall(__NR_waitid, ...), then it is possible for the
incorrect arguments to be passed to the syscall after it has been
restarted. This is because the syscall handler tries to shift all the
registers down one place in pt_regs so that when the syscall is restarted,
the "real" syscall is called instead. Unfortunately it only shifts the
arguments passed in registers, not the arguments on the user stack. This
causes the 4th argument to be duplicated when the syscall is restarted.

Fix by removing all the pt_regs shifting so that the indirect syscall
handler is called again when the syscall is restarted. The comment "some
syscalls like execve get their arguments from struct pt_regs" is long
out of date so this should now be safe.

Signed-off-by: James Cowgill <James.Cowgill@imgtec.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Tested-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15856/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
James Cowgill 2017-03-31 17:09:59 +01:00 committed by Ralf Baechle
parent 3d729deaf2
commit 5af2ed3669
2 changed files with 0 additions and 17 deletions
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11
arch/mips/kernel/scall32-o32.S
View File

@ -190,12 +190,6 @@ illegal_syscall:
sll t1, t0, 2
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
assume the worst case and shuffle around all potential arguments.
If you want performance, don't use indirect syscalls. */
move a0, a1 # shift argument registers
move a1, a2
@ -207,11 +201,6 @@ illegal_syscall:
sw t4, 16(sp)
sw t5, 20(sp)
sw t6, 24(sp)
sw a0, PT_R4(sp) # .. and push back a0 - a3, some
sw a1, PT_R5(sp) # syscalls expect them there
sw a2, PT_R6(sp)
sw a3, PT_R7(sp)
sw a3, PT_R26(sp) # update a3 for syscall restarting
jr t2
/* Unreached */

6
arch/mips/kernel/scall64-o32.S
View File

@ -198,7 +198,6 @@ LEAF(sys32_syscall)
dsll t1, t0, 3
beqz v0, einval
ld t2, sys32_call_table(t1) # syscall routine
sd a0, PT_R2(sp) # call routine directly on restart
move a0, a1 # shift argument registers
move a1, a2
@ -207,11 +206,6 @@ LEAF(sys32_syscall)
move a4, a5
move a5, a6
move a6, a7
sd a0, PT_R4(sp) # ... and push back a0 - a3, some
sd a1, PT_R5(sp) # syscalls expect them there
sd a2, PT_R6(sp)
sd a3, PT_R7(sp)
sd a3, PT_R26(sp) # update a3 for syscall restarting
jr t2
/* Unreached */