Re: [PATCH 3/3] perf, x86, lbr: Demand proper privileges for PERF_SAMPLE_BRANCH_KERNEL

On Wed, May 15, 2013 at 03:37:22PM +0200, Stephane Eranian wrote:

quoted

On Fri, May 3, 2013 at 2:11 PM, Peter Zijlstra [off-list ref] wrote:

quoted

We should always have proper privileges when requesting kernel data.

Cc: Andi Kleen <redacted>
Cc: eranian@google.com
Signed-off-by: Peter Zijlstra <redacted>
Link: http://lkml.kernel.org/n/tip-v0x9ky3ahzr6nm3c6ilwrili@git.kernel.org
---
 arch/x86/kernel/cpu/perf_event_intel_lbr.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c

@@ -318,8 +318,11 @@ static void intel_pmu_setup_sw_lbr_filte
        if (br_type & PERF_SAMPLE_BRANCH_USER)
                mask |= X86_BR_USER;

-       if (br_type & PERF_SAMPLE_BRANCH_KERNEL)
+       if (br_type & PERF_SAMPLE_BRANCH_KERNEL) {
+               if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
+                       return -EACCES;
                mask |= X86_BR_KERNEL;
+       }

This will prevent regular users from capturing kernel -> kernel branches.
But it won't prevent users from getting kernel -> user branches. Thus
some kernel address will still be captured. I guess they could be eliminated
by the sw_filter.

When using LBR priv level filtering, the filter applies to the branch target
only.

How about something like the below? It also adds the branch flags
Mikey wanted for PowerPC.

---
 arch/x86/kernel/cpu/perf_event_intel_lbr.c | 12 +++++++++---
 include/linux/perf_event.h                 | 10 +++++++---
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index d978353..f44d635 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c

@@ -585,17 +585,23 @@ intel_pmu_lbr_filter(struct cpu_hw_events *cpuc)
 
 		/* if type does not correspond, then discard */
 		if (type == X86_BR_NONE || (br_sel & type) != type) {
-			cpuc->lbr_entries[i].from = 0;
+			cpuc->lbr_entries[i].__delete = 1;
 			compress = true;
 		}
+
+		/* hide kernel addresses if we're not privileged  */
+		if (!(br_sel & X86_BR_KERNEL) && kernel_ip(from)) {
+			cpuc->lbr_entries[i].from = -1L;
+			cpuc->lbr_entries[i].invalid_from = 1;
+		}
 	}
 
 	if (!compress)
 		return;
 
-	/* remove all entries with from=0 */
+	/* remove all entries with __delete */
 	for (i = 0; i < cpuc->lbr_stack.nr; ) {
-		if (!cpuc->lbr_entries[i].from) {
+		if (cpuc->lbr_entries[i].__delete) {
 			j = i;
 			while (++j < cpuc->lbr_stack.nr)
 				cpuc->lbr_entries[j-1] = cpuc->lbr_entries[j];

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index f463a46..7acf1c9 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h

@@ -77,9 +77,13 @@ struct perf_raw_record {
 struct perf_branch_entry {
 	__u64	from;
 	__u64	to;
-	__u64	mispred:1,  /* target mispredicted */
-		predicted:1,/* target predicted */
-		reserved:62;
+	__u64	mispred:1,	/* target mispredicted		*/
+		predicted:1,	/* target predicted		*/
+		invalid_to:1,	/* @to isn't to be trusted	*/
+		invalid_from:1, /* @from isn't to be trusted	*/