From: peterz at infradead.org (Peter Zijlstra) Subject: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions Date: Fri, 3 May 2019 11:29:59 +0200 [thread overview] Message-ID: <20190503092959.GB2623@hirez.programming.kicks-ass.net> (raw) In-Reply-To: <20190502195052.0af473cf@gandalf.local.home> On Thu, May 02, 2019 at 07:50:52PM -0400, Steven Rostedt wrote: > On Thu, 2 May 2019 19:31:29 -0400 > Steven Rostedt <rostedt at goodmis.org> wrote: > > > Digging a little further, I pinpointed it out to being kretprobes. The > > problem I believe is the use of kernel_stack_pointer() which does some > > magic on x86_32. kretprobes uses this to hijack the return address of > > the function (much like the function graph tracer does). I do have code > > that would allow kretprobes to use the function graph tracer instead, > > but that's still in progress (almost done!). But still, we should not > > have this break the use of kernel_stack_pointer() either. > > > > Adding some printks in that code, it looks to be returning "®s->sp" > > which I think we changed. > > > > This appears to fix it! > > -- Steve > > diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c > index 4b8ee05dd6ad..600ead178bf4 100644 > --- a/arch/x86/kernel/ptrace.c > +++ b/arch/x86/kernel/ptrace.c > @@ -171,8 +171,12 @@ unsigned long kernel_stack_pointer(struct pt_regs *regs) > unsigned long sp = (unsigned long)®s->sp; > u32 *prev_esp; > > - if (context == (sp & ~(THREAD_SIZE - 1))) > + if (context == (sp & ~(THREAD_SIZE - 1))) { > + /* int3 code adds a gap */ > + if (sp == regs->sp - 5*4) > + return regs->sp; > return sp; > + } > > prev_esp = (u32 *)(context); > if (*prev_esp) OMG, WTF, ARGH... That code is fsck'ing horrible. I'd almost argue to always do the INT3 thing, just to avoid games like that. That said; for normal traps ®s->sp is indeed the previous context -- if it doesn't fall off the stack. Your hack detects the regular INT3 frame. Howver if regs->sp has been modified (int3_emulate_push, for example) your detectoring comes unstuck. Now, it is rather unlikely these two code paths interact, but just to be safe, something like so might be more reliable: diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 4b8ee05dd6ad..aceaad0cc9a9 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -163,6 +163,9 @@ static inline bool invalid_selector(u16 value) * stack pointer we fall back to regs as stack if no previous stack * exists. * + * There is a special case for INT3, there we construct a full pt_regs + * environment. We can detect this case by a high bit in regs->cs + * * This is valid only for kernel mode traps. */ unsigned long kernel_stack_pointer(struct pt_regs *regs) @@ -171,6 +174,9 @@ unsigned long kernel_stack_pointer(struct pt_regs *regs) unsigned long sp = (unsigned long)®s->sp; u32 *prev_esp; + if (regs->__csh & (1 << 13)) /* test CS_FROM_INT3 */ + return regs->sp; + if (context == (sp & ~(THREAD_SIZE - 1))) return sp; --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -388,6 +388,7 @@ #define CS_FROM_ENTRY_STACK (1 << 31) #define CS_FROM_USER_CR3 (1 << 30) +#define CS_FROM_INT3 (1 << 29) .macro SWITCH_TO_KERNEL_STACK @@ -1515,6 +1516,9 @@ ENTRY(int3) add $16, 12(%esp) # point sp back at the previous context + andl $0x0000ffff, 4(%esp) + orl $CS_FROM_INT3, 4(%esp) + pushl $-1 # orig_eax; mark as interrupt SAVE_ALL
WARNING: multiple messages have this Message-ID (diff)
From: peterz@infradead.org (Peter Zijlstra) Subject: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions Date: Fri, 3 May 2019 11:29:59 +0200 [thread overview] Message-ID: <20190503092959.GB2623@hirez.programming.kicks-ass.net> (raw) Message-ID: <20190503092959.2pFllVzEy2z7TdFn8_1Et8rgvzIHyAAk7h5gna_eJtI@z> (raw) In-Reply-To: <20190502195052.0af473cf@gandalf.local.home> On Thu, May 02, 2019@07:50:52PM -0400, Steven Rostedt wrote: > On Thu, 2 May 2019 19:31:29 -0400 > Steven Rostedt <rostedt@goodmis.org> wrote: > > > Digging a little further, I pinpointed it out to being kretprobes. The > > problem I believe is the use of kernel_stack_pointer() which does some > > magic on x86_32. kretprobes uses this to hijack the return address of > > the function (much like the function graph tracer does). I do have code > > that would allow kretprobes to use the function graph tracer instead, > > but that's still in progress (almost done!). But still, we should not > > have this break the use of kernel_stack_pointer() either. > > > > Adding some printks in that code, it looks to be returning "®s->sp" > > which I think we changed. > > > > This appears to fix it! > > -- Steve > > diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c > index 4b8ee05dd6ad..600ead178bf4 100644 > --- a/arch/x86/kernel/ptrace.c > +++ b/arch/x86/kernel/ptrace.c > @@ -171,8 +171,12 @@ unsigned long kernel_stack_pointer(struct pt_regs *regs) > unsigned long sp = (unsigned long)®s->sp; > u32 *prev_esp; > > - if (context == (sp & ~(THREAD_SIZE - 1))) > + if (context == (sp & ~(THREAD_SIZE - 1))) { > + /* int3 code adds a gap */ > + if (sp == regs->sp - 5*4) > + return regs->sp; > return sp; > + } > > prev_esp = (u32 *)(context); > if (*prev_esp) OMG, WTF, ARGH... That code is fsck'ing horrible. I'd almost argue to always do the INT3 thing, just to avoid games like that. That said; for normal traps ®s->sp is indeed the previous context -- if it doesn't fall off the stack. Your hack detects the regular INT3 frame. Howver if regs->sp has been modified (int3_emulate_push, for example) your detectoring comes unstuck. Now, it is rather unlikely these two code paths interact, but just to be safe, something like so might be more reliable: diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 4b8ee05dd6ad..aceaad0cc9a9 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -163,6 +163,9 @@ static inline bool invalid_selector(u16 value) * stack pointer we fall back to regs as stack if no previous stack * exists. * + * There is a special case for INT3, there we construct a full pt_regs + * environment. We can detect this case by a high bit in regs->cs + * * This is valid only for kernel mode traps. */ unsigned long kernel_stack_pointer(struct pt_regs *regs) @@ -171,6 +174,9 @@ unsigned long kernel_stack_pointer(struct pt_regs *regs) unsigned long sp = (unsigned long)®s->sp; u32 *prev_esp; + if (regs->__csh & (1 << 13)) /* test CS_FROM_INT3 */ + return regs->sp; + if (context == (sp & ~(THREAD_SIZE - 1))) return sp; --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -388,6 +388,7 @@ #define CS_FROM_ENTRY_STACK (1 << 31) #define CS_FROM_USER_CR3 (1 << 30) +#define CS_FROM_INT3 (1 << 29) .macro SWITCH_TO_KERNEL_STACK @@ -1515,6 +1516,9 @@ ENTRY(int3) add $16, 12(%esp) # point sp back at the previous context + andl $0x0000ffff, 4(%esp) + orl $CS_FROM_INT3, 4(%esp) + pushl $-1 # orig_eax; mark as interrupt SAVE_ALL
next prev parent reply other threads:[~2019-05-03 9:29 UTC|newest] Thread overview: 204+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <20190501202830.347656894@goodmis.org> 2019-05-01 20:28 ` [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions rostedt 2019-05-01 20:28 ` Steven Rostedt 2019-05-02 3:24 ` rostedt 2019-05-02 3:24 ` Steven Rostedt 2019-05-02 16:21 ` peterz 2019-05-02 16:21 ` Peter Zijlstra 2019-05-02 16:29 ` peterz 2019-05-02 16:29 ` Peter Zijlstra 2019-05-02 18:02 ` torvalds 2019-05-02 18:02 ` Linus Torvalds 2019-05-02 18:18 ` peterz 2019-05-02 18:18 ` Peter Zijlstra 2019-05-02 18:30 ` peterz 2019-05-02 18:30 ` Peter Zijlstra 2019-05-02 18:43 ` torvalds 2019-05-02 18:43 ` Linus Torvalds 2019-05-02 19:28 ` jikos 2019-05-02 19:28 ` Jiri Kosina 2019-05-02 20:25 ` luto 2019-05-02 20:25 ` Andy Lutomirski 2019-05-02 20:21 ` peterz 2019-05-02 20:21 ` Peter Zijlstra 2019-05-02 20:49 ` torvalds 2019-05-02 20:49 ` Linus Torvalds 2019-05-02 21:32 ` peterz 2019-05-02 21:32 ` Peter Zijlstra 2019-05-03 19:24 ` rostedt 2019-05-03 19:24 ` Steven Rostedt 2019-05-03 21:46 ` torvalds 2019-05-03 21:46 ` Linus Torvalds 2019-05-03 22:49 ` rostedt 2019-05-03 22:49 ` Steven Rostedt 2019-05-03 23:07 ` torvalds 2019-05-03 23:07 ` Linus Torvalds 2019-05-04 4:17 ` rostedt 2019-05-04 4:17 ` Steven Rostedt [not found] ` <CAHk-=wiuSFbv_rELND-BLWcP0GSZ0yF=xOAEcf61GE3bU9d=yg@mail.gmail.com> 2019-05-04 18:59 ` torvalds 2019-05-04 18:59 ` Linus Torvalds 2019-05-04 20:12 ` luto 2019-05-04 20:12 ` Andy Lutomirski 2019-05-04 20:28 ` torvalds 2019-05-04 20:28 ` Linus Torvalds 2019-05-04 20:36 ` torvalds 2019-05-04 20:36 ` Linus Torvalds 2019-05-03 22:55 ` luto 2019-05-03 22:55 ` Andy Lutomirski 2019-05-03 23:16 ` torvalds 2019-05-03 23:16 ` Linus Torvalds 2019-05-03 23:32 ` luto 2019-05-03 23:32 ` Andy Lutomirski 2019-05-02 22:52 ` rostedt 2019-05-02 22:52 ` Steven Rostedt 2019-05-02 23:31 ` rostedt 2019-05-02 23:31 ` Steven Rostedt 2019-05-02 23:50 ` rostedt 2019-05-02 23:50 ` Steven Rostedt 2019-05-03 1:51 ` [RFC][PATCH 1/2 v2] " rostedt 2019-05-03 1:51 ` Steven Rostedt 2019-05-03 9:29 ` peterz [this message] 2019-05-03 9:29 ` [RFC][PATCH 1/2] " Peter Zijlstra 2019-05-03 13:22 ` rostedt 2019-05-03 13:22 ` Steven Rostedt 2019-05-03 16:20 ` luto 2019-05-03 16:20 ` Andy Lutomirski 2019-05-03 16:31 ` rostedt 2019-05-03 16:31 ` Steven Rostedt 2019-05-03 16:35 ` peterz 2019-05-03 16:35 ` Peter Zijlstra 2019-05-03 16:44 ` luto 2019-05-03 16:44 ` Andy Lutomirski 2019-05-03 16:49 ` rostedt 2019-05-03 16:49 ` Steven Rostedt 2019-05-03 16:32 ` peterz 2019-05-03 16:32 ` Peter Zijlstra 2019-05-03 18:57 ` torvalds 2019-05-03 18:57 ` Linus Torvalds 2019-05-06 8:19 ` peterz 2019-05-06 8:19 ` Peter Zijlstra 2019-05-06 13:56 ` rostedt 2019-05-06 13:56 ` Steven Rostedt 2019-05-06 16:17 ` torvalds 2019-05-06 16:17 ` Linus Torvalds 2019-05-06 16:19 ` torvalds 2019-05-06 16:19 ` Linus Torvalds 2019-05-06 17:06 ` rostedt 2019-05-06 17:06 ` Steven Rostedt 2019-05-06 18:06 ` torvalds 2019-05-06 18:06 ` Linus Torvalds 2019-05-06 18:57 ` rostedt 2019-05-06 18:57 ` Steven Rostedt 2019-05-06 19:46 ` torvalds 2019-05-06 19:46 ` Linus Torvalds 2019-05-06 20:29 ` rostedt 2019-05-06 20:29 ` Steven Rostedt 2019-05-06 20:42 ` torvalds 2019-05-06 20:42 ` Linus Torvalds 2019-05-06 20:44 ` torvalds 2019-05-06 20:44 ` Linus Torvalds 2019-05-06 21:45 ` rostedt 2019-05-06 21:45 ` Steven Rostedt 2019-05-06 22:06 ` torvalds 2019-05-06 22:06 ` Linus Torvalds 2019-05-06 22:31 ` torvalds 2019-05-06 22:31 ` Linus Torvalds 2019-05-07 0:10 ` rostedt 2019-05-07 0:10 ` Steven Rostedt 2019-05-07 1:06 ` torvalds 2019-05-07 1:06 ` Linus Torvalds 2019-05-07 1:04 ` rostedt 2019-05-07 1:04 ` Steven Rostedt 2019-05-07 1:34 ` rostedt 2019-05-07 1:34 ` Steven Rostedt 2019-05-07 1:34 ` torvalds 2019-05-07 1:34 ` Linus Torvalds 2019-05-07 1:53 ` rostedt 2019-05-07 1:53 ` Steven Rostedt 2019-05-07 2:22 ` torvalds 2019-05-07 2:22 ` Linus Torvalds 2019-05-07 2:58 ` rostedt 2019-05-07 2:58 ` Steven Rostedt 2019-05-07 3:05 ` torvalds 2019-05-07 3:05 ` Linus Torvalds 2019-05-07 3:21 ` rostedt 2019-05-07 3:21 ` Steven Rostedt 2019-05-07 3:28 ` torvalds 2019-05-07 3:28 ` Linus Torvalds 2019-05-07 14:54 ` torvalds 2019-05-07 14:54 ` Linus Torvalds 2019-05-07 15:12 ` rostedt 2019-05-07 15:12 ` Steven Rostedt 2019-05-07 15:25 ` rostedt 2019-05-07 15:25 ` Steven Rostedt 2019-05-07 16:25 ` rostedt 2019-05-07 16:25 ` Steven Rostedt 2019-05-07 15:31 ` torvalds 2019-05-07 15:31 ` Linus Torvalds 2019-05-07 15:45 ` rostedt 2019-05-07 15:45 ` Steven Rostedt 2019-05-07 16:34 ` peterz 2019-05-07 16:34 ` Peter Zijlstra 2019-05-07 17:08 ` torvalds 2019-05-07 17:08 ` Linus Torvalds 2019-05-07 17:21 ` jpoimboe 2019-05-07 17:21 ` Josh Poimboeuf 2019-05-07 21:24 ` rostedt 2019-05-07 21:24 ` Steven Rostedt 2019-05-08 4:50 ` torvalds 2019-05-08 4:50 ` Linus Torvalds 2019-05-08 16:37 ` rostedt 2019-05-08 16:37 ` Steven Rostedt 2019-05-07 17:38 ` peterz 2019-05-07 17:38 ` Peter Zijlstra 2019-05-07 9:51 ` peterz 2019-05-07 9:51 ` Peter Zijlstra 2019-05-07 14:48 ` luto 2019-05-07 14:48 ` Andy Lutomirski 2019-05-07 14:57 ` torvalds 2019-05-07 14:57 ` Linus Torvalds 2019-05-07 14:13 ` mhiramat 2019-05-07 14:13 ` Masami Hiramatsu 2019-05-07 17:15 ` mhiramat 2019-05-07 17:15 ` Masami Hiramatsu 2019-05-06 14:22 ` peterz 2019-05-06 14:22 ` Peter Zijlstra 2019-05-07 8:57 ` peterz 2019-05-07 8:57 ` Peter Zijlstra 2019-05-07 9:18 ` David.Laight 2019-05-07 9:18 ` David Laight 2019-05-07 11:30 ` peterz 2019-05-07 11:30 ` Peter Zijlstra 2019-05-07 12:57 ` David.Laight 2019-05-07 12:57 ` David Laight 2019-05-07 13:14 ` rostedt 2019-05-07 13:14 ` Steven Rostedt 2019-05-07 14:50 ` David.Laight 2019-05-07 14:50 ` David Laight 2019-05-07 14:57 ` rostedt 2019-05-07 14:57 ` Steven Rostedt 2019-05-07 15:46 ` David.Laight 2019-05-07 15:46 ` David Laight 2019-05-07 13:32 ` peterz 2019-05-07 13:32 ` Peter Zijlstra 2019-05-07 9:27 ` peterz 2019-05-07 9:27 ` Peter Zijlstra 2019-05-07 12:27 ` rostedt 2019-05-07 12:27 ` Steven Rostedt 2019-05-07 12:41 ` peterz 2019-05-07 12:41 ` Peter Zijlstra 2019-05-07 12:54 ` rostedt 2019-05-07 12:54 ` Steven Rostedt 2019-05-07 17:22 ` masami.hiramatsu 2019-05-07 17:22 ` Masami Hiramatsu 2019-05-07 14:28 ` peterz 2019-05-07 14:28 ` Peter Zijlstra 2019-05-02 20:48 ` rostedt 2019-05-02 20:48 ` Steven Rostedt 2019-05-06 15:14 ` jpoimboe 2019-05-06 15:14 ` Josh Poimboeuf 2019-05-01 20:28 ` [RFC][PATCH 2/2] ftrace/x86: Emulate call function while updating in breakpoint handler rostedt 2019-05-01 20:28 ` Steven Rostedt 2019-05-03 10:22 ` [RFC][PATCH 1.5/2] x86: Add int3_emulate_call() selftest peterz 2019-05-03 10:22 ` Peter Zijlstra 2019-05-03 18:46 ` rostedt 2019-05-03 18:46 ` Steven Rostedt
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20190503092959.GB2623@hirez.programming.kicks-ass.net \ --to=linux-kselftest@vger.kernel.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).