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 [gthelen: manual backport to 5.4] --- kernel/events/core.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c index 1993a741d2dc..6ffe3d3e7b06 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6536,7 +6536,6 @@ void perf_output_sample(struct perf_output_handle *handle, static u64 perf_virt_to_phys(u64 virt) { u64 phys_addr = 0; - struct page *p = NULL;

if (!virt) return 0; @@ -6555,14 +6554,15 @@ 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_pages_fast(virt, 1, 0, &p) == 1) + if (__get_user_pages_fast(virt, 1, 0, &p) == 1) { phys_addr = page_to_phys(p) + virt % PAGE_SIZE; + put_page(p); + } pagefault_enable(); } - - if (p) - put_page(p); }

return phys_addr;