From: peterz@infradead.org
To: Jin Yao <yao.jin@linux.intel.com>
Cc: mingo@redhat.com, oleg@redhat.com, acme@kernel.org,
jolsa@kernel.org, Linux-kernel@vger.kernel.org,
ak@linux.intel.com, kan.liang@intel.com, yao.jin@intel.com,
alexander.shishkin@linux.intel.com, mark.rutland@arm.com
Subject: Re: [PATCH v1 2/2] perf/core: Fake regs for leaked kernel samples
Date: Tue, 4 Aug 2020 13:49:00 +0200 [thread overview]
Message-ID: <20200804114900.GI2657@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200731025617.16243-2-yao.jin@linux.intel.com>
On Fri, Jul 31, 2020 at 10:56:17AM +0800, Jin Yao wrote:
> @@ -6973,7 +6973,8 @@ static struct perf_callchain_entry __empty_callchain = { .nr = 0, };
> struct perf_callchain_entry *
> perf_callchain(struct perf_event *event, struct pt_regs *regs)
> {
> - bool kernel = !event->attr.exclude_callchain_kernel;
> + bool kernel = !event->attr.exclude_callchain_kernel &&
> + !event->attr.exclude_kernel;
This seems weird; how can we get there. Also it seems to me that if you
have !exclude_callchain_kernel you already have permission for kernel
bits, so who cares.
> bool user = !event->attr.exclude_callchain_user;
> /* Disallow cross-task user callchains. */
> bool crosstask = event->ctx->task && event->ctx->task != current;
> @@ -6988,12 +6989,39 @@ perf_callchain(struct perf_event *event, struct pt_regs *regs)
> return callchain ?: &__empty_callchain;
> }
>
> +static struct pt_regs *leak_check(struct perf_event_header *header,
> + struct perf_event *event,
> + struct pt_regs *regs)
> +{
> + struct pt_regs *regs_fake = NULL;
> +
> + if (event->attr.exclude_kernel && !user_mode(regs)) {
> + if (!(current->flags & PF_KTHREAD)) {
> + regs_fake = task_pt_regs(current);
> + if (!user_mode(regs_fake)) {
> + regs_fake = NULL;
> + instruction_pointer_set(regs, -1L);
> + }
> + } else
> + instruction_pointer_set(regs, -1L);
That violates coding style, also:
if (!(current->flags & PF_KTHREAD)) {
regs_fake = task_pt_regs(current);
if (!user_mode(regs_fake)) /* is this not a BUG? */
regs_fake = NULL;
}
if (!regs_fake)
instruction_pointer_set(regs, -1L);
Seems simpler to me.
> + if ((header->misc & PERF_RECORD_MISC_CPUMODE_MASK) ==
> + PERF_RECORD_MISC_KERNEL) {
> + header->misc &= ~PERF_RECORD_MISC_CPUMODE_MASK;
> + header->misc |= PERF_RECORD_MISC_USER;
> + }
Why the conditional? At this point it had better be unconditionally
user, no?
headers->misc &= ~PERF_RECORD_MISC_CPUMODE_MASK;
headers->misc |= PERF_RECORD_MISC_USER;
> + }
> +
> + return regs_fake;
> +}
next prev parent reply other threads:[~2020-08-04 11:54 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-31 2:56 [PATCH v1 1/2] Missing instruction_pointer_set() instances Jin Yao
2020-07-31 2:56 ` [PATCH v1 2/2] perf/core: Fake regs for leaked kernel samples Jin Yao
2020-08-04 11:49 ` peterz [this message]
2020-08-05 2:15 ` Jin, Yao
2020-08-05 12:44 ` peterz
2020-08-05 12:57 ` peterz
2020-08-06 2:26 ` Jin, Yao
2020-08-06 9:18 ` peterz
2020-08-06 9:24 ` peterz
2020-08-07 5:32 ` Jin, Yao
2020-08-06 11:00 ` peterz
2020-08-07 6:24 ` Jin, Yao
2020-08-07 9:02 ` peterz
2020-08-10 2:03 ` Jin, Yao
2020-08-07 5:23 ` Jin, Yao
2020-08-11 7:50 ` Jin, Yao
2020-08-11 7:59 ` Peter Zijlstra
2020-08-11 8:31 ` Jin, Yao
2020-08-11 8:45 ` Peter Zijlstra
2020-08-12 3:52 ` Jin, Yao
2020-08-12 7:25 ` Like Xu
2020-08-04 11:31 ` [PATCH v1 1/2] Missing instruction_pointer_set() instances peterz
2020-08-05 0:26 ` Jin, Yao
2020-08-04 21:31 ` Max Filippov
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