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

Commit 46e12c07b3 (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: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Ralf Baechle 2015-07-08 04:49:10 +02:00
parent 0bb383a2d8
commit 7928eb0370
2 changed files with 52 additions and 18 deletions
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37
arch/mips/kernel/scall32-o32.S
View File

@ -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
*/

33
arch/mips/kernel/scall64-o32.S
View File

@ -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