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Commit 5af2ed36 authored by James Cowgill's avatar James Cowgill Committed by Ralf Baechle
Browse files

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out of date so this should now be safe.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: default avatarJames Cowgill <James.Cowgill@imgtec.com>
Reviewed-by: default avatarJames Hogan <james.hogan@imgtec.com>
Tested-by: default avatarJames Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/15856/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 3d729dea

arch/mips/kernel/scall32-o32.S

+0 −11
Original line number Diff line number Diff line
@@ -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 */

arch/mips/kernel/scall64-o32.S

+0 −6
Original line number Diff line number Diff line
@@ -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 */