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

Namhyung Kim
2025-03-17T15:57:23Z

On Mon, Mar 17, 2025 at 11:10:48AM +0100, Borislav Petkov wrote:
> 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)) {
> > + throttle = perf_event_account_interrupt(event);
> > + goto out;
> > + }
>
> Did anyone build this?

Oops, sorry about this. I fixed it locally but sent the one before
adding the change. Will send v2.

Thanks,
Namhyung

>
> arch/x86/events/amd/ibs.c: In function ‘perf_ibs_handle_irq’:
> arch/x86/events/amd/ibs.c:1291:63: error: macro "access_ok" requires 2 arguments, but only 1 given
> 1291 | event->attr.exclude_kernel && !access_ok(data.addr)) {
> | ^
> In file included from ./arch/x86/include/asm/uaccess.h:25,
> from ./include/linux/uaccess.h:12,
> from ./include/linux/sched/task.h:13,
> from ./include/linux/sched/signal.h:9,
> from ./include/linux/ptrace.h:7,
> from ./include/uapi/asm-generic/bpf_perf_event.h:4,
> from ./arch/x86/include/generated/uapi/asm/bpf_perf_event.h:1,
> from ./include/uapi/linux/bpf_perf_event.h:11,
> from ./include/linux/perf_event.h:18,
> from arch/x86/events/amd/ibs.c:9:
> ./include/asm-generic/access_ok.h:45: note: macro "access_ok" defined here
> 45 | #define access_ok(addr, size) likely(__access_ok(addr, size))
> |
> arch/x86/events/amd/ibs.c:1291:44: error: ‘access_ok’ undeclared (first use in this function)
> 1291 | event->attr.exclude_kernel && !access_ok(data.addr)) {
> | ^~~~~~~~~
> arch/x86/events/amd/ibs.c:1291:44: note: each undeclared identifier is reported only once for each function it appears in
> make[5]: *** [scripts/Makefile.build:207: arch/x86/events/amd/ibs.o] Error 1
> make[4]: *** [scripts/Makefile.build:465: arch/x86/events/amd] Error 2
> make[4]: *** Waiting for unfinished jobs....
> make[3]: *** [scripts/Makefile.build:465: arch/x86/events] Error 2
> make[3]: *** Waiting for unfinished jobs....
> make[2]: *** [scripts/Makefile.build:465: arch/x86] Error 2
> make[2]: *** Waiting for unfinished jobs....
> make[1]: *** [/mnt/kernel/kernel/6th/linux/Makefile:1997: .] Error 2
> make: *** [Makefile:251: __sub-make] Error 2
>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette