perf/core: Avoid put_page() when GUP fails
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The following commit has been merged into the perf/urgent branch of tip:
Commit-ID: 4716023a8f6a0f4a28047f14dd7ebdc319606b84 Gitweb: https://git.kernel.org/tip/4716023a8f6a0f4a28047f14dd7ebdc319606b84 Author: Greg Thelen <[email protected]> AuthorDate: Wed, 10 Nov 2021 18:18:14 -08:00 Committer: Peter Zijlstra <[email protected]> CommitterDate: Thu, 11 Nov 2021 13:09:34 +01:00
perf/core: Avoid put_page() when GUP fails
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.
--- kernel/events/core.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
kernel/events/core.c +5 -5
@@ -7154,7 +7154,6 @@ 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 ;
@@ -7173,14 +7172,15 @@ 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;