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Commit 7928eb03 authored by Ralf Baechle's avatar Ralf Baechle
Browse files

MIPS: O32: Do not handle require 32 bytes from the stack to be readable. 



Commit 46e12c07 (MIPS: O32 / 32-bit:
Always copy 4 stack arguments.) change the O32 syscall handler to always
load four arguments from the userspace stack even for syscalls that
require fewer or no arguments to be copied.  This removes a large table
from kernel space and need to maintain it.  It appeared that it was ok
the implementation chosen requires 16 bytes of readable stack space
above the user stack pointer.

Turned out a few threading implementations munmap the user stack before
the thread exits resulting in errors due to the unreadable stack.

We now treat any failed load as a if the loaded value was zero and let
the actual syscall deal with the situation.

Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 0bb383a2

arch/mips/kernel/scall32-o32.S

+27 −10
Original line number Diff line number Diff line
@@ -73,10 +73,11 @@ NESTED(handle_sys, PT_SIZE, sp) 
	.set    noreorder

	.set	nomacro



1:	user_lw(t5, 16(t0))		# argument #5 from usp

4:	user_lw(t6, 20(t0))		# argument #6 from usp

3:	user_lw(t7, 24(t0))		# argument #7 from usp

2:	user_lw(t8, 28(t0))		# argument #8 from usp

load_a4: user_lw(t5, 16(t0))		# argument #5 from usp

load_a5: user_lw(t6, 20(t0))		# argument #6 from usp

load_a6: user_lw(t7, 24(t0))		# argument #7 from usp

load_a7: user_lw(t8, 28(t0))		# argument #8 from usp

loads_done:



	sw	t5, 16(sp)		# argument #5 to ksp

	sw	t6, 20(sp)		# argument #6 to ksp
@@ -85,10 +86,10 @@ NESTED(handle_sys, PT_SIZE, sp) 
	.set	pop



	.section __ex_table,"a"

	PTR	1b,bad_stack

	PTR	2b,bad_stack

	PTR	3b,bad_stack

	PTR	4b,bad_stack

	PTR	load_a4, bad_stack_a4

	PTR	load_a5, bad_stack_a5

	PTR	load_a6, bad_stack_a6

	PTR	load_a7, bad_stack_a7

	.previous



	lw	t0, TI_FLAGS($28)	# syscall tracing enabled?
@@ -153,8 +154,8 @@ syscall_trace_entry: 
/* ------------------------------------------------------------------------ */



	/*

	 * The stackpointer for a call with more than 4 arguments is bad.

	 * We probably should handle this case a bit more drastic.

	 * Our open-coded access area sanity test for the stack pointer

	 * failed. We probably should handle this case a bit more drastic.

	 */

bad_stack:

	li	v0, EFAULT
@@ -163,6 +164,22 @@ bad_stack: 
	sw	t0, PT_R7(sp)

	j	o32_syscall_exit



bad_stack_a4:

	li	t5, 0

	b	load_a5



bad_stack_a5:

	li	t6, 0

	b	load_a6



bad_stack_a6:

	li	t7, 0

	b	load_a7



bad_stack_a7:

	li	t8, 0

	b	loads_done



	/*

	 * The system call does not exist in this kernel

	 */

arch/mips/kernel/scall64-o32.S

+25 −8
Original line number Diff line number Diff line
@@ -69,16 +69,17 @@ NESTED(handle_sys, PT_SIZE, sp) 
	daddu	t1, t0, 32

	bltz	t1, bad_stack



1:	lw	a4, 16(t0)		# argument #5 from usp

2:	lw	a5, 20(t0)		# argument #6 from usp

3:	lw	a6, 24(t0)		# argument #7 from usp

4:	lw	a7, 28(t0)		# argument #8 from usp (for indirect syscalls)

load_a4: lw	a4, 16(t0)		# argument #5 from usp

load_a5: lw	a5, 20(t0)		# argument #6 from usp

load_a6: lw	a6, 24(t0)		# argument #7 from usp

load_a7: lw	a7, 28(t0)		# argument #8 from usp

loads_done:



	.section __ex_table,"a"

	PTR	1b, bad_stack

	PTR	2b, bad_stack

	PTR	3b, bad_stack

	PTR	4b, bad_stack

	PTR	load_a4, bad_stack_a4

	PTR	load_a5, bad_stack_a5

	PTR	load_a6, bad_stack_a6

	PTR	load_a7, bad_stack_a7

	.previous



	li	t1, _TIF_WORK_SYSCALL_ENTRY
@@ -167,6 +168,22 @@ bad_stack: 
	sd	t0, PT_R7(sp)

	j	o32_syscall_exit



bad_stack_a4:

	li	a4, 0

	b	load_a5



bad_stack_a5:

	li	a5, 0

	b	load_a6



bad_stack_a6:

	li	a6, 0

	b	load_a7



bad_stack_a7:

	li	a7, 0

	b	loads_done



not_o32_scall:

	/*

	 * This is not an o32 compatibility syscall, pass it on