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perf/core: Avoid put_page() when GUP fails
commit4716023a8f
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:fc7ce9c74c
("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>
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1 changed files with 5 additions and 5 deletions
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@ -6110,7 +6110,6 @@ void perf_output_sample(struct perf_output_handle *handle,
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static u64 perf_virt_to_phys(u64 virt)
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{
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u64 phys_addr = 0;
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struct page *p = NULL;
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if (!virt)
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return 0;
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@ -6129,14 +6128,15 @@ static u64 perf_virt_to_phys(u64 virt)
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* If failed, leave phys_addr as 0.
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*/
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if (current->mm != NULL) {
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struct page *p;
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pagefault_disable();
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if (__get_user_pages_fast(virt, 1, 0, &p) == 1)
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if (__get_user_pages_fast(virt, 1, 0, &p) == 1) {
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phys_addr = page_to_phys(p) + virt % PAGE_SIZE;
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put_page(p);
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}
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pagefault_enable();
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}
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if (p)
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put_page(p);
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}
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return phys_addr;
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