Re: [tip:tracing/kprobes] x86: kretprobe-booster interrupt emulation code fix

Masami Hiramatsu
2009-03-24T23:25:27Z

Bharata B Rao wrote:
> On Tue, Mar 24, 2009 at 02:13:59PM +0100, Ingo Molnar wrote:
>> * Masami Hiramatsu <mhiramat@redhat.com> wrote:
>>
>>> regs->ip = trampoline_address;
>>> regs->orig_ax = ~0UL;
>>> + regs->gs = 0;
>> hm, this wont build on 32-bit.
>
> I guess you meant 64 bit. Yes I see that it fails to build on x86_64.
>
> Regards,
> Bharata.

Thanks, here I updated my patch.
---

Fix interrupt emulation code in kretprobe-booster according to
pt_regs update (es/ds change and gs adding).

This issue has been reported on systemtap-bugzilla:
http://sources.redhat.com/bugzilla/show_bug.cgi?id=9965

On a -tip kernel on x86_32, kretprobe_example (from samples) triggers the
following backtrace when its retprobing a class of functions that cause a
copy_from/to_user().

BUG: sleeping function called from invalid context at mm/memory.c:3196
in_atomic(): 0, irqs_disabled(): 1, pid: 2286, name: cat
1 lock held by cat/2286:
#0: (&p->lock){+.+.+.}, at: [<c04b4eb1>] seq_read+0x35/0x31d
irq event stamp: 1613
hardirqs last enabled at (1613): [<c06b5914>] _spin_unlock_irqrestore+0x3c/0x48
hardirqs last disabled at (1612): [<c06b5a7f>] _spin_lock_irqsave+0x1a/0x3f
softirqs last enabled at (1610): [<c04348c5>] __do_softirq+0x164/0x183
softirqs last disabled at (1603): [<c0404d2c>] do_softirq+0x68/0xc8
Pid: 2286, comm: cat Not tainted 2.6.29-rc8-tip-acde #1
Call Trace:
[<c0429017>] __might_sleep+0xde/0xe3
[<c048c6e1>] might_fault+0x1f/0x80
[<c0535b87>] copy_to_user+0x2f/0x106
[<c04b5120>] seq_read+0x2a4/0x31d
[<c04d4882>] proc_reg_read+0x6a/0x84
[<c04b4e7c>] ? seq_read+0x0/0x31d
[<c04d4882>] ? proc_reg_read+0x6a/0x84
[<c04d4818>] ? proc_reg_read+0x0/0x84
[<c04a1f73>] vfs_read+0x90/0xef
[<c04a208b>] sys_read+0x4e/0x75
[<c044d338>] ? trace_hardirqs_on_caller+0x11d/0x141
[<c0402fc4>] sysenter_do_call+0x12/0x38
[<c0402fc4>] ? sysenter_do_call+0x12/0x38

Steps to recreate:
1. put kretprobe on meminfo_proc_show.
2. cat /proc/meminfo
3. Your dmesg should have the above trace.

Problem doesn't happen with 2.6.29-rc8.

This is a kretprobe booster bug on x86_32. Commit ccbeed3a modifies the
pt_regs, the kretprobe_trampoline() part of the kretprobe booster needs to be
updated to handle the gs register.

changes from v1:
- Don't set regs->gs if CONFIG_X86_64=y.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
---

arch/x86/kernel/kprobes.c | 17 +++++++++--------
1 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 55b9461..7b5169d 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -638,13 +638,13 @@ static void __used __kprobes kretprobe_trampoline_holder(void)
#else
" pushf\n"
/*
- * Skip cs, ip, orig_ax.
+ * Skip cs, ip, orig_ax and gs.
* trampoline_handler() will plug in these values
*/
- " subl $12, %esp\n"
+ " subl $16, %esp\n"
" pushl %fs\n"
- " pushl %ds\n"
" pushl %es\n"
+ " pushl %ds\n"
" pushl %eax\n"
" pushl %ebp\n"
" pushl %edi\n"
@@ -655,10 +655,10 @@ static void __used __kprobes kretprobe_trampoline_holder(void)
" movl %esp, %eax\n"
" call trampoline_handler\n"
/* Move flags to cs */
- " movl 52(%esp), %edx\n"
- " movl %edx, 48(%esp)\n"
+ " movl 56(%esp), %edx\n"
+ " movl %edx, 52(%esp)\n"
/* Replace saved flags with true return address. */
- " movl %eax, 52(%esp)\n"
+ " movl %eax, 56(%esp)\n"
" popl %ebx\n"
" popl %ecx\n"
" popl %edx\n"
@@ -666,8 +666,8 @@ static void __used __kprobes kretprobe_trampoline_holder(void)
" popl %edi\n"
" popl %ebp\n"
" popl %eax\n"
- /* Skip ip, orig_ax, es, ds, fs */
- " addl $20, %esp\n"
+ /* Skip ds, es, fs, gs, orig_ax and ip */
+ " addl $24, %esp\n"
" popf\n"
#endif
" ret\n");
@@ -691,6 +691,7 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
regs->cs = __KERNEL_CS;
#else
regs->cs = __KERNEL_CS | get_kernel_rpl();
+ regs->gs = 0;
#endif
regs->ip = trampoline_address;
regs->orig_ax = ~0UL;

--
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com