[RESEND PATCH] perf/x86/intel: Fix PEBS-via-PT reload base value for Extended PEBS

Like Xu
2021-06-21T03:47:27Z

If we use the "PEBS-via-PT" feature on a platform that supports
extended PBES, like this:

perf record -c 10000 \
-e '{intel_pt/branch=0/,branch-instructions/aux-output/p}' uname

we will encounter the following call trace:

[ 250.906542] unchecked MSR access error: WRMSR to 0x14e1 (tried to write
0x0000000000000000) at rIP: 0xffffffff88073624 (native_write_msr+0x4/0x20)
[ 250.920779] Call Trace:
[ 250.923508] intel_pmu_pebs_enable+0x12c/0x190
[ 250.928359] intel_pmu_enable_event+0x346/0x390
[ 250.933300] x86_pmu_start+0x64/0x80
[ 250.937231] x86_pmu_enable+0x16a/0x2f0
[ 250.941434] perf_event_exec+0x144/0x4c0
[ 250.945731] begin_new_exec+0x650/0xbf0
[ 250.949933] load_elf_binary+0x13e/0x1700
[ 250.954321] ? lock_acquire+0xc2/0x390
[ 250.958430] ? bprm_execve+0x34f/0x8a0
[ 250.962544] ? lock_is_held_type+0xa7/0x120
[ 250.967118] ? find_held_lock+0x32/0x90
[ 250.971321] ? sched_clock_cpu+0xc/0xb0
[ 250.975527] bprm_execve+0x33d/0x8a0
[ 250.979452] do_execveat_common.isra.0+0x161/0x1d0
[ 250.984673] __x64_sys_execve+0x33/0x40
[ 250.988877] do_syscall_64+0x3d/0x80
[ 250.992806] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 250.998302] RIP: 0033:0x7fbc971d82fb
[ 251.002235] Code: Unable to access opcode bytes at RIP 0x7fbc971d82d1.
[ 251.009303] RSP: 002b:00007fffb8aed808 EFLAGS: 00000202 ORIG_RAX: 000000000000003b
[ 251.017478] RAX: ffffffffffffffda RBX: 00007fffb8af2f00 RCX: 00007fbc971d82fb
[ 251.025187] RDX: 00005574792aac50 RSI: 00007fffb8af2f00 RDI: 00007fffb8aed810
[ 251.032901] RBP: 00007fffb8aed970 R08: 0000000000000020 R09: 00007fbc9725c8b0
[ 251.040613] R10: 6d6c61632f6d6f63 R11: 0000000000000202 R12: 00005574792aac50
[ 251.048327] R13: 00007fffb8af35f0 R14: 00005574792aafdf R15: 00005574792aafe7

This is because the target reload msr address is calculated
based on the wrong base msr and the target reload msr value
is accessed from ds->pebs_event_reset[] with the wrong offset.

According to Intel SDM Table 2-14, for extended PBES feature,
the reload msr for MSR_IA32_FIXED_CTRx should be based on
MSR_RELOAD_FIXED_CTRx.

For fixed counters, let's fix it by overriding the reload msr
address and its value, thus avoiding out-of-bounds access.

Fixes: 42880f726c66("perf/x86/intel: Support PEBS output to PT")
Signed-off-by: Like Xu <likexu@tencent.com>
---
arch/x86/events/intel/ds.c | 20 ++++++++++++++------
1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index 1ec8fd311f38..8647713276a7 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1187,6 +1187,9 @@ static void intel_pmu_pebs_via_pt_enable(struct perf_event *event)
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct hw_perf_event *hwc = &event->hw;
struct debug_store *ds = cpuc->ds;
+ u64 value = ds->pebs_event_reset[hwc->idx];
+ u32 base = MSR_RELOAD_PMC0;
+ unsigned int idx = hwc->idx;

if (!is_pebs_pt(event))
return;
@@ -1196,7 +1199,12 @@ static void intel_pmu_pebs_via_pt_enable(struct perf_event *event)

cpuc->pebs_enabled |= PEBS_OUTPUT_PT;

- wrmsrl(MSR_RELOAD_PMC0 + hwc->idx, ds->pebs_event_reset[hwc->idx]);
+ if (hwc->idx >= INTEL_PMC_IDX_FIXED) {
+ base = MSR_RELOAD_FIXED_CTR0;
+ idx = hwc->idx - INTEL_PMC_IDX_FIXED;
+ value = ds->pebs_event_reset[MAX_PEBS_EVENTS + idx];
+ }
+ wrmsrl(base + idx, value);
}

void intel_pmu_pebs_enable(struct perf_event *event)
@@ -1204,6 +1212,7 @@ void intel_pmu_pebs_enable(struct perf_event *event)
struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
struct hw_perf_event *hwc = &event->hw;
struct debug_store *ds = cpuc->ds;
+ unsigned int idx = hwc->idx;

hwc->config &= ~ARCH_PERFMON_EVENTSEL_INT;

@@ -1222,19 +1231,18 @@ void intel_pmu_pebs_enable(struct perf_event *event)
}
}

+ if (idx >= INTEL_PMC_IDX_FIXED)
+ idx = MAX_PEBS_EVENTS + (idx - INTEL_PMC_IDX_FIXED);
+
/*
* Use auto-reload if possible to save a MSR write in the PMI.
* This must be done in pmu::start(), because PERF_EVENT_IOC_PERIOD.
*/
if (hwc->flags & PERF_X86_EVENT_AUTO_RELOAD) {
- unsigned int idx = hwc->idx;
-
- if (idx >= INTEL_PMC_IDX_FIXED)
- idx = MAX_PEBS_EVENTS + (idx - INTEL_PMC_IDX_FIXED);
ds->pebs_event_reset[idx] =
(u64)(-hwc->sample_period) & x86_pmu.cntval_mask;
} else {
- ds->pebs_event_reset[hwc->idx] = 0;
+ ds->pebs_event_reset[idx] = 0;
}

intel_pmu_pebs_via_pt_enable(event);
--
2.30.1 (Apple Git-130)