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Subject[PATCH 2/2] perf/x86/intel/bts: Fix the use of page_private()
Date
Commit

8062382c8dbe2 ("perf/x86/intel/bts: Add BTS PMU driver")

uses page_private(page) without checking the PagePrivate(page) first,
which seems like a potential bug, considering that page->private aliases
with other stuff in struct page.

Fix this by checking PagePrivate() first.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Fixes: 8062382c8dbe2 ("perf/x86/intel/bts: Add BTS PMU driver")
---
arch/x86/events/intel/bts.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
index d53b4fb86d87..9e4da1c5a129 100644
--- a/arch/x86/events/intel/bts.c
+++ b/arch/x86/events/intel/bts.c
@@ -63,9 +63,17 @@ struct bts_buffer {

static struct pmu bts_pmu;

+static int buf_nr_pages(struct page *page)
+{
+ if (!PagePrivate(page))
+ return 1;
+
+ return 1 << page_private(page);
+}
+
static size_t buf_size(struct page *page)
{
- return 1 << (PAGE_SHIFT + page_private(page));
+ return 1 << (PAGE_SHIFT + buf_nr_pages(page));
}

static void *
@@ -83,7 +91,7 @@ bts_buffer_setup_aux(struct perf_event *event, void **pages,
/* count all the high order buffers */
for (pg = 0, nbuf = 0; pg < nr_pages;) {
page = virt_to_page(pages[pg]);
- pg += 1 << page_private(page);
+ pg += buf_nr_pages(page);
nbuf++;
}

@@ -107,7 +115,7 @@ bts_buffer_setup_aux(struct perf_event *event, void **pages,
unsigned int __nr_pages;

page = virt_to_page(pages[pg]);
- __nr_pages = PagePrivate(page) ? 1 << page_private(page) : 1;
+ __nr_pages = buf_nr_pages(page);
buf->buf[nbuf].page = page;
buf->buf[nbuf].offset = offset;
buf->buf[nbuf].displacement = (pad ? BTS_RECORD_SIZE - pad : 0);
--
2.24.0
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