Re: [tip: perf/urgent] perf/x86: Check data address for IBS software filter

Peter Zijlstra
2025-03-17T10:15:07Z

On Mon, Mar 17, 2025 at 09:15:05AM -0000, tip-bot2 for Namhyung Kim wrote:
> The following commit has been merged into the perf/urgent branch of tip:
>
> Commit-ID: b0be17d8108bf3448a58be319d085155a128cf3a
> Gitweb: https://git.kernel.org/tip/b0be17d8108bf3448a58be319d085155a128cf3a
> Author: Namhyung Kim <namhyung@kernel.org>
> AuthorDate: Mon, 17 Mar 2025 01:10:58 -07:00
> Committer: Ingo Molnar <mingo@kernel.org>
> CommitterDate: Mon, 17 Mar 2025 10:04:31 +01:00
>
> perf/x86: Check data address for IBS software filter
>
> The IBS software filter is filtering 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 mode 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>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Link: https://lore.kernel.org/r/20250317081058.1794729-1-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 e7a8b87..24985c7 100644
> --- a/arch/x86/events/amd/ibs.c
> +++ b/arch/x86/events/amd/ibs.c
> @@ -1147,6 +1147,13 @@ fail:
> 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)) {

If only you'd looked at all the other filter code :/ everybody uses
kernel_ip() helper for this, not access_ok().

> + 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