[PATCH] KVM: x86/pmu: Prevent any host user from enabling PEBS for profiling guest

Like Xu
2023-11-29T09:51:24Z

From: Like Xu <likexu@tencent.com>

Stop using PEBS counters on host to profiling guest. Limit the range of
enabled PEBS counters to only those counters enabled from the guest PEBS
emulation perspective.

If there is a perf-record agent on host that uses perf-tools events like
"cpu-cycles:GP" (G for attr.exclude_host, P for max precise event counter)
to capture guest performance events, then the guest will be hanged. This is
because Intel DS-based PEBS buffer is addressed using the 64-bit linear
address of the current {p/v}CPU context based on MSR_IA32_DS_AREA.

Any perf user using PEBS counters to profile guest on host is, in perf/core
implementation details, trying to set bits on cpuc->intel_ctrl_guest_mask
and arr[pebs_enable].guest, much like the guest PEBS emulation behaviour.
But the subsequent PEBS memory write, regardless of whether guest PEBS is
enabled, can overshoot guest entry and corrupt guest memory.

Profiling guest via PEBS-DS buffer on host is not supported at this time.
Fix this by filtering the real configured value of arr[pebs_enable].guest
with the emulated state of guest enabled PEBS counters, under the condition
of none cross-mapped PEBS counters.

Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Fixes: c59a1f106f5c ("KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS")
Signed-off-by: Like Xu <likexu@tencent.com>
---
arch/x86/events/intel/core.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index a08f794a0e79..17afd504c35b 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -4103,13 +4103,19 @@ static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr, void *data)
.guest = pebs_mask & ~cpuc->intel_ctrl_host_mask,
};

+ /* In any case, clear guest PEBS bits first. */
+ arr[global_ctrl].guest &= ~arr[pebs_enable].guest;
+
if (arr[pebs_enable].host) {
/* Disable guest PEBS if host PEBS is enabled. */
arr[pebs_enable].guest = 0;
} else {
/* Disable guest PEBS thoroughly for cross-mapped PEBS counters. */
arr[pebs_enable].guest &= ~kvm_pmu->host_cross_mapped_mask;
- arr[global_ctrl].guest &= ~kvm_pmu->host_cross_mapped_mask;
+
+ /* Prevent any host user from enabling PEBS for profiling guest. */
+ arr[pebs_enable].guest &= (kvm_pmu->pebs_enable & kvm_pmu->global_ctrl);
+
/* Set hw GLOBAL_CTRL bits for PEBS counter when it runs for guest */
arr[global_ctrl].guest |= arr[pebs_enable].guest;
}

base-commit: 6803fb00772cc50cd59a66bd8caaee5c84b13fcf
--
2.43.0