[PATCH] perf/x86: Check data address for IBS software filter

Namhyung Kim
2025-03-17T08:11:00Z

IBS software filter was to filter kernel samples for regular users in
PMI handler. It checks the instruction address in the IBS register to
determine if it was in the kernel more or not.

But it turns out that it's possible to report a kernel data address even
if the instruction address belongs to the user space. Matteo Rizzo
found that when an instruction raises an exception, IBS can report some
kernel data address like IDT while holding the faulting instruction's
RIP. To prevent an information leak, it should double check if the data
address in PERF_SAMPLE_DATA is in the kernel space as well.

Suggested-by: Matteo Rizzo <matteorizzo@google.com>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
arch/x86/events/amd/ibs.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index 7b52b8e3a185157f..8b3b76fad587b3ff 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -1286,6 +1286,13 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)
if (perf_ibs == &perf_ibs_op)
perf_ibs_parse_ld_st_data(event->attr.sample_type, &ibs_data, &data);

+ if ((event->attr.config2 & IBS_SW_FILTER_MASK) &&
+ (event->attr.sample_type & PERF_SAMPLE_ADDR) &&
+ event->attr.exclude_kernel && !access_ok(data.addr)) {
+ throttle = perf_event_account_interrupt(event);
+ goto out;
+ }
+
/*
* rip recorded by IbsOpRip will not be consistent with rsp and rbp
* recorded as part of interrupt regs. Thus we need to use rip from
--
2.49.0.rc1.451.g8f38331e32-goog