[PATCH 5.10 20/21] perf/core: Avoid put_page() when GUP fails

Greg Kroah-Hartman
2021-11-19T17:38:51Z

From: Greg Thelen <gthelen@google.com>

commit 4716023a8f6a0f4a28047f14dd7ebdc319606b84 upstream.

PEBS PERF_SAMPLE_PHYS_ADDR events use perf_virt_to_phys() to convert PMU
sampled virtual addresses to physical using get_user_page_fast_only()
and page_to_phys().

Some get_user_page_fast_only() error cases return false, indicating no
page reference, but still initialize the output page pointer with an
unreferenced page. In these error cases perf_virt_to_phys() calls
put_page(). This causes page reference count underflow, which can lead
to unintentional page sharing.

Fix perf_virt_to_phys() to only put_page() if get_user_page_fast_only()
returns a referenced page.

Fixes: fc7ce9c74c3ad ("perf/core, x86: Add PERF_SAMPLE_PHYS_ADDR")
Signed-off-by: Greg Thelen <gthelen@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211111021814.757086-1-gthelen@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/events/core.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7036,7 +7036,6 @@ void perf_output_sample(struct perf_outp
static u64 perf_virt_to_phys(u64 virt)
{
u64 phys_addr = 0;
- struct page *p = NULL;

if (!virt)
return 0;
@@ -7055,14 +7054,15 @@ static u64 perf_virt_to_phys(u64 virt)
* If failed, leave phys_addr as 0.
*/
if (current->mm != NULL) {
+ struct page *p;
+
pagefault_disable();
- if (get_user_page_fast_only(virt, 0, &p))
+ if (get_user_page_fast_only(virt, 0, &p)) {
phys_addr = page_to_phys(p) + virt % PAGE_SIZE;
+ put_page(p);
+ }
pagefault_enable();
}
-
- if (p)
- put_page(p);
}

return phys_addr;