The previous change documents that cleanup_return_instances() can't
always detect the dead frames, the stack can grow. But there is one
special case which imho worth fixing: arch_uretprobe_is_alive() can
return true when the stack didn't actually grow, but the next "call"
insn uses the already invalidated frame.
Test-case:
#include <stdio.h>
#include <setjmp.h>
jmp_buf jmp;
int nr = 1024;
void func_2(void)
{
if (--nr == 0)
return;
longjmp(jmp, 1);
}
void func_1(void)
{
setjmp(jmp);
func_2();
}
int main(void)
{
func_1();
return 0;
}
If you ret-probe func_1() and func_2() prepare_uretprobe() hits the
MAX_URETPROBE_DEPTH limit and "return" from func_2() is not reported.
Add the new "bool on_call" argument to arch_uretprobe_is_alive().
prepare_uretprobe()->cleanup_return_instances() path passes "true"
when we know that we can do a more strict check to detect the dead
frames: chained == F. In this case "sp" points to the new ret-addr,
so every frame which uses the same "sp" must be dead.
Note: arch_uretprobe_is_alive() could also re-read *sp and check if
this word is still trampoline_vaddr. This could obviously improve the
logic, but I'd like to avoid another copy_from_user() especially in
a case when we can't avoid the false "alive == T" positives.
Signed-off-by: Oleg Nesterov <[email protected]>
---
arch/x86/kernel/uprobes.c | 10 ++++++++--
include/linux/uprobes.h | 3 ++-
kernel/events/uprobes.c | 12 +++++++-----
3 files changed, 17 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 868dc47..f0ace39 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -929,7 +929,13 @@ arch_uretprobe_hijack_return_addr(struct arch_uretprobe
*auret,
return -1;
}
-bool arch_uretprobe_is_alive(struct arch_uretprobe *auret, struct pt_regs
*regs)
+bool arch_uretprobe_is_alive(struct arch_uretprobe *auret,
+ bool on_call, struct pt_regs *regs)
{
- return regs->sp <= auret->sp;
+ unsigned long sp = regs->sp;
+
+ if (on_call) /* ->sp was just decremented by "call" insn */
+ sp += sizeof_long();
+
+ return sp <= auret->sp;
}
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 1ed7502..9907be4 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -129,7 +129,8 @@ extern int arch_uprobe_exception_notify(struct
notifier_block *self, unsigned l
extern void arch_uprobe_abort_xol(struct arch_uprobe *aup, struct pt_regs
*regs);
extern unsigned long arch_uretprobe_hijack_return_addr(struct arch_uretprobe
*auret,
unsigned long trampoline_vaddr, struct
pt_regs *regs);
-extern bool arch_uretprobe_is_alive(struct arch_uretprobe *auret, struct
pt_regs *regs);
+extern bool arch_uretprobe_is_alive(struct arch_uretprobe *auret,
+ bool on_call, struct pt_regs *regs);
extern bool arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs);
extern void arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
void *src, unsigned long len);
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index b6433fb..ec697da 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1522,10 +1522,11 @@ static unsigned long get_trampoline_vaddr(void)
return trampoline_vaddr;
}
-static void cleanup_return_instances(struct uprobe_task *utask, struct pt_regs
*regs)
+static void cleanup_return_instances(struct uprobe_task *utask,
+ bool on_call, struct pt_regs *regs)
{
struct return_instance *ri = utask->return_instances;
- while (ri && !arch_uretprobe_is_alive(&ri->auret, regs)) {
+ while (ri && !arch_uretprobe_is_alive(&ri->auret, on_call, regs)) {
ri = free_ret_instance(ri);
utask->depth--;
}
@@ -1587,7 +1588,7 @@ static void prepare_uretprobe(struct uprobe *uprobe,
struct pt_regs *regs)
ri->chained = chained;
if (utask->depth) /* drop the entries invalidated by longjmp() */
- cleanup_return_instances(utask, regs);
+ cleanup_return_instances(utask, !chained, regs);
utask->depth++;
ri->next = utask->return_instances;
@@ -1815,7 +1816,7 @@ static void handle_trampoline(struct pt_regs *regs)
* could hit this trampoline on return. TODO: sigaltstack().
*/
next = find_next_ret_chain(ri);
- valid = !next || arch_uretprobe_is_alive(&next->auret, regs);
+ valid = !next || arch_uretprobe_is_alive(&next->auret, false,
regs);
instruction_pointer_set(regs, ri->orig_ret_vaddr);
do {
@@ -1840,7 +1841,8 @@ bool __weak arch_uprobe_ignore(struct arch_uprobe *aup,
struct pt_regs *regs)
return false;
}
-bool __weak arch_uretprobe_is_alive(struct arch_uretprobe *auret, struct
pt_regs *regs)
+bool __weak arch_uretprobe_is_alive(struct arch_uretprobe *auret,
+ bool on_call, struct pt_regs *regs)
{
return true;
}
--
1.5.5.1
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