From 145ebf95fb346528dd276c3e23324609e5f4d3f6 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Mon, 29 Jan 2018 18:15:33 -0800 Subject: [PATCH] kaiser: fix intel_bts perf crashes MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Vince reported perf_fuzzer quickly locks up on 4.15-rc7 with PTI; Robert reported Bad RIP with KPTI and Intel BTS also on 4.15-rc7: honggfuzz -f /tmp/somedirectorywithatleastonefile \ --linux_perf_bts_edge -s -- /bin/true (honggfuzz from https://github.com/google/honggfuzz) crashed with BUG: unable to handle kernel paging request at ffff9d3215100000 (then narrowed it down to perf record --per-thread -e intel_bts//u -- /bin/ls). The intel_bts driver does not use the 'normal' BTS buffer which is exposed through kaiser_add_mapping(), but instead uses the memory allocated for the perf AUX buffer. This obviously comes apart when using PTI, because then the kernel mapping, which includes that AUX buffer memory, disappears while switched to user page tables. Easily fixed in old-Kaiser backports, by applying kaiser_add_mapping() to those pages; perhaps not so easy for upstream, where 4.15-rc8 commit 99a9dc98ba52 ("x86,perf: Disable intel_bts when PTI") disables for now. Slightly reorganized surrounding code in bts_buffer_setup_aux(), so it can better match bts_buffer_free_aux(): free_aux with an #ifdef to avoid the loop when PTI is off, but setup_aux needs to loop anyway (and kaiser_add_mapping() is cheap when PTI config is off or "pti=off"). Reported-by: Vince Weaver Reported-by: Robert Święcki Analyzed-by: Peter Zijlstra Analyzed-by: Stephane Eranian Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Andy Lutomirski Cc: Alexander Shishkin Cc: Linus Torvalds Cc: Vince Weaver Cc: stable@vger.kernel.org Cc: Jiri Kosina Signed-off-by: Hugh Dickins Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/perf_event_intel_bts.c | 44 ++++++++++++++++------ 1 file changed, 33 insertions(+), 11 deletions(-) diff --git a/arch/x86/kernel/cpu/perf_event_intel_bts.c b/arch/x86/kernel/cpu/perf_event_intel_bts.c index 2cad71d1b14c..5af11c46d0b9 100644 --- a/arch/x86/kernel/cpu/perf_event_intel_bts.c +++ b/arch/x86/kernel/cpu/perf_event_intel_bts.c @@ -22,6 +22,7 @@ #include #include #include +#include #include #include @@ -67,6 +68,23 @@ static size_t buf_size(struct page *page) return 1 << (PAGE_SHIFT + page_private(page)); } +static void bts_buffer_free_aux(void *data) +{ +#ifdef CONFIG_PAGE_TABLE_ISOLATION + struct bts_buffer *buf = data; + int nbuf; + + for (nbuf = 0; nbuf < buf->nr_bufs; nbuf++) { + struct page *page = buf->buf[nbuf].page; + void *kaddr = page_address(page); + size_t page_size = buf_size(page); + + kaiser_remove_mapping((unsigned long)kaddr, page_size); + } +#endif + kfree(data); +} + static void * bts_buffer_setup_aux(int cpu, void **pages, int nr_pages, bool overwrite) { @@ -103,29 +121,33 @@ bts_buffer_setup_aux(int cpu, void **pages, int nr_pages, bool overwrite) buf->real_size = size - size % BTS_RECORD_SIZE; for (pg = 0, nbuf = 0, offset = 0, pad = 0; nbuf < buf->nr_bufs; nbuf++) { - unsigned int __nr_pages; + void *kaddr = pages[pg]; + size_t page_size; + + page = virt_to_page(kaddr); + page_size = buf_size(page); + + if (kaiser_add_mapping((unsigned long)kaddr, + page_size, __PAGE_KERNEL) < 0) { + buf->nr_bufs = nbuf; + bts_buffer_free_aux(buf); + return NULL; + } - page = virt_to_page(pages[pg]); - __nr_pages = PagePrivate(page) ? 1 << page_private(page) : 1; buf->buf[nbuf].page = page; buf->buf[nbuf].offset = offset; buf->buf[nbuf].displacement = (pad ? BTS_RECORD_SIZE - pad : 0); - buf->buf[nbuf].size = buf_size(page) - buf->buf[nbuf].displacement; + buf->buf[nbuf].size = page_size - buf->buf[nbuf].displacement; pad = buf->buf[nbuf].size % BTS_RECORD_SIZE; buf->buf[nbuf].size -= pad; - pg += __nr_pages; - offset += __nr_pages << PAGE_SHIFT; + pg += page_size >> PAGE_SHIFT; + offset += page_size; } return buf; } -static void bts_buffer_free_aux(void *data) -{ - kfree(data); -} - static unsigned long bts_buffer_offset(struct bts_buffer *buf, unsigned int idx) { return buf->buf[idx].offset + buf->buf[idx].displacement;