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SubjectRe: [PATCH v15 04/10] arm64: Kprobes with single stepping support
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On 20/07/16 17:28, Catalin Marinas wrote:
> On Wed, Jul 20, 2016 at 05:09:28PM +0100, Marc Zyngier wrote:
>> +static inline unsigned long min_stack_size(unsigned long addr)
>> +{
>> + unsigned long size;
>> + struct kprobe_ctlblk *ctl;
>> +
>> + if (on_irq_stack(addr, raw_smp_processor_id()))
>> + size = IRQ_STACK_PTR(raw_smp_processor_id()) - addr;
>> + else
>> + size = (unsigned long)current_thread_info() + THREAD_START_SP - addr;
>> +
>> + return min(size, sizeof(ctl->jprobes_stack));
>> +}
>
> We could drop the local ctl pointer:
>
> return min(size, sizeof(((struct kprobe_ctlblk *)0)->jprobes_stack));
>
> If you add a log, I'll push the patch on top of the kprobes branch.

Here you go:

----8<----
From 0d120f95b3348e1946d8a789c7147f316c27ea6b Mon Sep 17 00:00:00 2001
From: Marc Zyngier <marc.zyngier@arm.com>
Date: Wed, 20 Jul 2016 17:36:42 +0100
Subject: [PATCH] arm64: kprobes: Fix overflow when saving stack

The MIN_STACK_SIZE macro tries evaluate how much stack space needs
to be saved in the jprobes_stack array, sized at 128 bytes.

When using the IRQ stack, said macro can happily return up to
IRQ_STACK_SIZE, which is 16kB. Mayhem follows.

This patch fixes things by getting rid of the crazy macro and
limiting the copy to be at most the size of the jprobes_stack
array, no matter which stack we're on.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm64/kernel/probes/kprobes.c | 22 ++++++++++++++--------
1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index 823cf92..87a24f6 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -34,12 +34,6 @@

#include "decode-insn.h"

-#define MIN_STACK_SIZE(addr) (on_irq_stack(addr, raw_smp_processor_id()) ? \
- min((unsigned long)IRQ_STACK_SIZE, \
- IRQ_STACK_PTR(raw_smp_processor_id()) - (addr)) : \
- min((unsigned long)MAX_STACK_SIZE, \
- (unsigned long)current_thread_info() + THREAD_START_SP - (addr)))
-
void jprobe_return_break(void);

DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
@@ -48,6 +42,18 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
static void __kprobes
post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);

+static inline unsigned long min_stack_size(unsigned long addr)
+{
+ unsigned long size;
+
+ if (on_irq_stack(addr, raw_smp_processor_id()))
+ size = IRQ_STACK_PTR(raw_smp_processor_id()) - addr;
+ else
+ size = (unsigned long)current_thread_info() + THREAD_START_SP - addr;
+
+ return min(size, FIELD_SIZEOF(struct kprobe_ctlblk, jprobes_stack));
+}
+
static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
{
/* prepare insn slot */
@@ -495,7 +501,7 @@ int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
* the argument area.
*/
memcpy(kcb->jprobes_stack, (void *)stack_ptr,
- MIN_STACK_SIZE(stack_ptr));
+ min_stack_size(stack_ptr));

instruction_pointer_set(regs, (unsigned long) jp->entry);
preempt_disable();
@@ -547,7 +553,7 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
unpause_graph_tracing();
*regs = kcb->jprobe_saved_regs;
memcpy((void *)stack_addr, kcb->jprobes_stack,
- MIN_STACK_SIZE(stack_addr));
+ min_stack_size(stack_addr));
preempt_enable_no_resched();
return 1;
}
--
2.1.4
Thanks,

M.
--
Jazz is not dead. It just smells funny...

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