ARM: 6005/1: arm: kprobes: fix register corruption with jprobes
Current implementation of jprobes allocates empty pt_regs from the
stack which is then passed to kprobe_handler() and eventually to
singlestep(). Now when instruction being simulated is STMFD (like
in normal function prologues without CONFIG_FRAME_POINTER), stores
using SP actually write over top of the fabricated pt_regs
structure.
This can be reproduced for example by using LKDTM module:
# modprobe lkdtm
# mount -t debugfs none /sys/kernel/debug
# echo PANIC > /sys/kernel/debug/provoke-crash/INT_HW_IRQ_EN
after this, it fails with corrupted registers (before the requested crash would occur):
lkdtm: Crash point INT_HW_IRQ_EN of type PANIC hit, trigger in 9 rounds
lkdtm: Crash point INT_HW_IRQ_EN of type PANIC hit, trigger in 8 rounds
Internal error: Oops - undefined instruction: 0 [#1]
last sysfs file: /sys/devices/platform/serial8250.0/sleep_timeout
Modules linked in: lkdtm
CPU: 0 Not tainted (2.6.34-rc2 #69)
PC is at irq_desc+0x1638/0xeeb0
LR is at 0x25
pc : [<c050b428>] lr : [<00000025>] psr: c80a0013
sp : ce94bd60 ip : c050b3e8 fp : a0000013
r10: c0aa453c r9 : cf5d4000 r8 : ce9a1822
r7 : c050b424 r6 : 00000025 r5 : c039d8f8 r4 : c050b3e8
r3 : 00000001 r2 : cf4d0440 r1 : c039d8f8 r0 : 00000020
Flags: NZcv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
Control: 10c5387d Table: 8e804019 DAC: 00000015
Process sh (pid: 496, stack limit = 0xce94a2e8)
Stack: (0xce94bd60 to 0xce94c000)
[...]
Code: 000002cd 00000000 00000000 00000001 (dead4ead)
---[ end trace 2b46d5f2b682f370 ]---
Kernel panic - not syncing: Fatal exception in interrupt
This patch allocates enough space (2 * sizeof(struct pt_regs)) from
the stack to prevent such corruption.
Signed-off-by: Mika Westerberg <ext-mika.1.westerberg@nokia.com>
Acked-by: Nicolas Pitre <nico@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/kernel/kprobes.c b/arch/arm/kernel/kprobes.c
index 60c62c3..610e0f5 100644
--- a/arch/arm/kernel/kprobes.c
+++ b/arch/arm/kernel/kprobes.c
@@ -393,6 +393,14 @@
/*
* Setup an empty pt_regs. Fill SP and PC fields as
* they're needed by longjmp_break_handler.
+ *
+ * We allocate some slack between the original SP and start of
+ * our fabricated regs. To be precise we want to have worst case
+ * covered which is STMFD with all 16 regs so we allocate 2 *
+ * sizeof(struct_pt_regs)).
+ *
+ * This is to prevent any simulated instruction from writing
+ * over the regs when they are accessing the stack.
*/
"sub sp, %0, %1 \n\t"
"ldr r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t"
@@ -410,7 +418,7 @@
"ldmia sp, {r0 - pc} \n\t"
:
: "r" (kcb->jprobe_saved_regs.ARM_sp),
- "I" (sizeof(struct pt_regs)),
+ "I" (sizeof(struct pt_regs) * 2),
"J" (offsetof(struct pt_regs, ARM_sp)),
"J" (offsetof(struct pt_regs, ARM_pc)),
"J" (offsetof(struct pt_regs, ARM_cpsr))