From db087ef69a2b155ae001665bf0b3806abde7ee34 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Tue, 21 Jul 2015 15:40:28 +0200 Subject: 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 #include 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 Signed-off-by: Oleg Nesterov Acked-by: Srikar Dronamraju Acked-by: Anton Arapov Cc: Andy Lutomirski Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20150721134028.GA4786@redhat.com Signed-off-by: Ingo Molnar --- kernel/events/uprobes.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) (limited to 'kernel/events') diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index df5661a44e35..0f370ef57a02 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; } -- cgit v1.2.3