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Subject[PATCH] perf/x86: fix 32-bit perf user callgraph collection
Date
A basic perf callgraph record operation causes an immediate panic on a
32-bit kernel compiled with CONFIG_CC_STACKPROTECTOR:

$ perf record -g ls
Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: c0404fbd

CPU: 0 PID: 998 Comm: ls Not tainted 4.7.0-rc5+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.1-1.fc24 04/01/2014
c0dd5967 ff7afe1c 00000086 f41dbc2c c07445a0 464c457f f41dbca8 f41dbc44
c05646f4 f41dbca8 464c457f f41dbca8 464c457f f41dbc54 c04625be c0ce56fc
c0404fbd f41dbc88 c0404fbd b74668f0 f41dc000 00000000 c0000000 00000000
Call Trace:
[<c07445a0>] dump_stack+0x58/0x78
[<c05646f4>] panic+0x8e/0x1c6
[<c04625be>] __stack_chk_fail+0x1e/0x30
[<c0404fbd>] ? perf_callchain_user+0x22d/0x230
[<c0404fbd>] perf_callchain_user+0x22d/0x230
[<c055f89f>] get_perf_callchain+0x1ff/0x270
[<c055f988>] perf_callchain+0x78/0x90
[<c055c7eb>] perf_prepare_sample+0x24b/0x370
[<c055c934>] perf_event_output_forward+0x24/0x70
[<c05531c0>] __perf_event_overflow+0xa0/0x210
[<c0550a93>] ? cpu_clock_event_read+0x43/0x50
[<c0553431>] perf_swevent_hrtimer+0x101/0x180
[<c0456235>] ? kmap_atomic_prot+0x35/0x140
[<c056dc69>] ? get_page_from_freelist+0x279/0x950
[<c058fdd8>] ? vma_interval_tree_remove+0x158/0x230
[<c05939f4>] ? wp_page_copy.isra.82+0x2f4/0x630
[<c05a050d>] ? page_add_file_rmap+0x1d/0x50
[<c0565611>] ? unlock_page+0x61/0x80
[<c0566755>] ? filemap_map_pages+0x305/0x320
[<c059769f>] ? handle_mm_fault+0xb7f/0x1560
[<c074cbeb>] ? timerqueue_del+0x1b/0x70
[<c04cfefe>] ? __remove_hrtimer+0x2e/0x60
[<c04d017b>] __hrtimer_run_queues+0xcb/0x2a0
[<c0553330>] ? __perf_event_overflow+0x210/0x210
[<c04d0a2a>] hrtimer_interrupt+0x8a/0x180
[<c043ecc2>] local_apic_timer_interrupt+0x32/0x60
[<c043f643>] smp_apic_timer_interrupt+0x33/0x50
[<c0b0cd38>] apic_timer_interrupt+0x34/0x3c
Kernel Offset: disabled
---[ end Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: c0404fbd

The panic is caused by the fact that perf_callchain_user() mistakenly
assumes it's 64-bit only and ends up corrupting the stack.

Fixes: 75925e1ad7f5 ("perf/x86: Optimize stack walk user accesses")
Cc: stable@vger.kernel.org
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
arch/x86/events/core.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 929655d..d265e9eb 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2342,7 +2342,7 @@ void
perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
{
struct stack_frame frame;
- const void __user *fp;
+ const unsigned long __user *fp;

if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
/* TODO: We don't support guest os callchain now */
@@ -2355,7 +2355,7 @@ perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs
if (regs->flags & (X86_VM_MASK | PERF_EFLAGS_VM))
return;

- fp = (void __user *)regs->bp;
+ fp = (unsigned long __user *)regs->bp;

perf_callchain_store(entry, regs->ip);

@@ -2368,16 +2368,19 @@ perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs
pagefault_disable();
while (entry->nr < entry->max_stack) {
unsigned long bytes;
+
frame.next_frame = NULL;
frame.return_address = 0;

- if (!access_ok(VERIFY_READ, fp, 16))
+ if (!access_ok(VERIFY_READ, fp, sizeof(*fp) * 2))
break;

- bytes = __copy_from_user_nmi(&frame.next_frame, fp, 8);
+ bytes = __copy_from_user_nmi(&frame.next_frame, fp,
+ sizeof(*fp));
if (bytes != 0)
break;
- bytes = __copy_from_user_nmi(&frame.return_address, fp+8, 8);
+ bytes = __copy_from_user_nmi(&frame.return_address,
+ fp + 1, sizeof(*fp));
if (bytes != 0)
break;

--
2.7.4
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