This is a note to let you know that I've just added the patch titled perf/core: Avoid put_page() when GUP fails to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: perf-core-avoid-put_page-when-gup-fails.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 4716023a8f6a0f4a28047f14dd7ebdc319606b84 Mon Sep 17 00:00:00 2001 From: Greg Thelen <gthelen@xxxxxxxxxx> Date: Wed, 10 Nov 2021 18:18:14 -0800 Subject: perf/core: Avoid put_page() when GUP fails From: Greg Thelen <gthelen@xxxxxxxxxx> 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@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20211111021814.757086-1-gthelen@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/events/core.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6424,7 +6424,6 @@ 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; @@ -6443,14 +6442,15 @@ 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; Patches currently in stable-queue which might be from gthelen@xxxxxxxxxx are queue-4.19/perf-core-avoid-put_page-when-gup-fails.patch