arm64: kprobes: Fix overflow when saving stack

commit ab4c1325d4bf111a590a1f773e3d93bde7f40201 upstream.

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.

[dave.long@linaro.org: Since there is no irq_stack in this kernel version
this fix is not strictly necessary, but is included for completeness.]

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: David A. Long <dave.long@linaro.org>

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index a9b274c99519a7bfb7702864b0d80bcc42059cda..b1189741dbb086dbc9175d8e6bf1e8e6496a4e49 100644 (file)
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -34,9 +34,6 @@
 
 #include "decode-insn.h"
 
-#define MIN_STACK_SIZE(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;
@@ -45,6 +42,15 @@ 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;
+
+       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 */
@@ -492,7 +498,7 @@ 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();
@@ -545,7 +551,7 @@ 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;
 }