linux-kernel - [PATCH 1/2] perf/x86/utils: fix uninitialized var in get_branch

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Date:   Wed, 28 Sep 2022 11:40:42 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, sandipan.das@....com, ananth.narayan@....com,
        ravi.bangoria@....com
Subject: [PATCH 1/2] perf/x86/utils: fix uninitialized var in get_branch_type()

offset is passed as a pointer and on certain call path is not set by the
function. If the caller does not re-initialize offset between calls, value
could be inherited between calls. Prevent this by initializing offset on each
call.
This impacts the code in amd_pmu_lbr_filter() which does
   for(i=0; ...) {
       ret = get_branch_type_fused(..., &offset);
       if (offset)
          lbr_entries[i].from += offset;
   }

Signed-off-by: Stephane Eranian <eranian@...gle.com>
---
 arch/x86/events/utils.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/events/utils.c b/arch/x86/events/utils.c
index 5f5617afde79..76b1f8bb0fd5 100644
--- a/arch/x86/events/utils.c
+++ b/arch/x86/events/utils.c
@@ -94,6 +94,10 @@ static int get_branch_type(unsigned long from, unsigned long to, int abort,
 	u8 buf[MAX_INSN_SIZE];
 	int is64 = 0;
 
+	/* make sure we initialize offset */
+	if (offset)
+		*offset = 0;
+
 	to_plm = kernel_ip(to) ? X86_BR_KERNEL : X86_BR_USER;
 	from_plm = kernel_ip(from) ? X86_BR_KERNEL : X86_BR_USER;
 
-- 
2.37.3.998.g577e59143f-goog