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Date: Fri, 31 Jul 2015 07:01:07 -0700
From: tip-bot for Oleg Nesterov <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: mingo@...nel.org, peterz@...radead.org, hpa@...or.com,
panand@...hat.com, luto@...capital.net, arapov@...il.com,
torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
oleg@...hat.com, tglx@...utronix.de, srikar@...ux.vnet.ibm.com
Subject: [tip:perf/core] uprobes/x86: Make arch_uretprobe_is_alive(
RP_CHECK_CALL) more clever
Commit-ID: db087ef69a2b155ae001665bf0b3806abde7ee34
Gitweb: http://git.kernel.org/tip/db087ef69a2b155ae001665bf0b3806abde7ee34
Author: Oleg Nesterov <oleg@...hat.com>
AuthorDate: Tue, 21 Jul 2015 15:40:28 +0200
Committer: Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 31 Jul 2015 10:38:06 +0200
uprobes/x86: Make arch_uretprobe_is_alive(RP_CHECK_CALL) more clever
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.
When we know that the new call is not chained, we can do the
more strict check. In this case "sp" points to the new ret-addr,
so every frame which uses the same "sp" must be dead. The only
complication is that arch_uretprobe_is_alive() needs to know was
it chained or not, so we add the new RP_CHECK_CHAIN_CALL enum
and change prepare_uretprobe() to pass RP_CHECK_CALL only if
!chained.
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 would like to avoid another
copy_from_user() especially in the case when we can't avoid the
false "alive == T" positives.
Tested-by: Pratyush Anand <panand@...hat.com>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Acked-by: Anton Arapov <arapov@...il.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20150721134028.GA4786@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
arch/x86/kernel/uprobes.c | 5 ++++-
include/linux/uprobes.h | 1 +
kernel/events/uprobes.c | 14 +++++++-------
3 files changed, 12 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index acf8b90..bf4db6e 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -989,5 +989,8 @@ arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs
bool arch_uretprobe_is_alive(struct return_instance *ret, enum rp_check ctx,
struct pt_regs *regs)
{
- return regs->sp <= ret->stack;
+ if (ctx == RP_CHECK_CALL) /* sp was just decremented by "call" insn */
+ return regs->sp < ret->stack;
+ else
+ return regs->sp <= ret->stack;
}
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index c0a5402..0bdc72f 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -104,6 +104,7 @@ struct return_instance {
enum rp_check {
RP_CHECK_CALL,
+ RP_CHECK_CHAIN_CALL,
RP_CHECK_RET,
};
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index df5661a..0f370ef 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1511,10 +1511,11 @@ 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 chained,
+ struct pt_regs *regs)
{
struct return_instance *ri = utask->return_instances;
- enum rp_check ctx = RP_CHECK_CALL;
+ enum rp_check ctx = chained ? RP_CHECK_CHAIN_CALL : RP_CHECK_CALL;
while (ri && !arch_uretprobe_is_alive(ri, ctx, regs)) {
ri = free_ret_instance(ri);
@@ -1528,7 +1529,7 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
struct return_instance *ri;
struct uprobe_task *utask;
unsigned long orig_ret_vaddr, trampoline_vaddr;
- bool chained = false;
+ bool chained;
if (!get_xol_area())
return;
@@ -1554,14 +1555,15 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
goto fail;
/* drop the entries invalidated by longjmp() */
- cleanup_return_instances(utask, regs);
+ chained = (orig_ret_vaddr == trampoline_vaddr);
+ cleanup_return_instances(utask, chained, regs);
/*
* We don't want to keep trampoline address in stack, rather keep the
* original return address of first caller thru all the consequent
* instances. This also makes breakpoint unwrapping easier.
*/
- if (orig_ret_vaddr == trampoline_vaddr) {
+ if (chained) {
if (!utask->return_instances) {
/*
* This situation is not possible. Likely we have an
@@ -1570,8 +1572,6 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
uprobe_warn(current, "handle tail call");
goto fail;
}
-
- chained = true;
orig_ret_vaddr = utask->return_instances->orig_ret_vaddr;
}
--
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