71 lines
2.3 KiB
Diff
71 lines
2.3 KiB
Diff
From bc8698fd7ed13a629a8ec3cb2a89bd74f9d8b5c0 Mon Sep 17 00:00:00 2001
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From: Giuseppe Ottaviano <ott@fb.com>
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Date: Sun, 20 Mar 2016 00:28:03 +0000
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Subject: [PATCH] x86_64: fix mincore_validate
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The detection logic introduced in 28f33c8ce0b654cf31d6beda9a612870662f3c56 is
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broken, because it tests mincore using an address that is almost certainly not
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page-aligned. straces confirms that msync is used all the time.
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This patch fixes the logic by page-aligning the test pointer. strace now shows
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that mincore is actually used. Furthermore, the return value of mincore is not
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sufficient to assess whether the address can be safely dereferenced: we should
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also check that the pages are mapped, through the passed mvec array. This patch
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also adds this verification.
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Tested on a system where unwinding a stack across a JNI boundary would cause
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sporadic segfaults; no more crashes were observed after the patch.
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---
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src/x86_64/Ginit.c | 24 ++++++++++++++++++++++--
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1 file changed, 22 insertions(+), 2 deletions(-)
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--- src/x86_64/Ginit.c
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+++ src/x86_64/Ginit.c
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@@ -30,6 +30,7 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
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#include <config.h>
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#endif
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+#include <errno.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/mman.h>
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@@ -81,7 +82,21 @@ static int msync_validate (void *addr, size_t len)
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static int mincore_validate (void *addr, size_t len)
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{
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unsigned char mvec[2]; /* Unaligned access may cross page boundary */
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- return mincore (addr, len, mvec);
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+ size_t i;
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+
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+ /* mincore could fail with EAGAIN but we conservatively return -1
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+ instead of looping. */
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+ if (mincore (addr, len, mvec) != 0)
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+ {
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+ return -1;
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+ }
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+
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+ for (i = 0; i < (len + PAGE_SIZE - 1) / PAGE_SIZE; i++)
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+ {
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+ if (!(mvec[i] & 1)) return -1;
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+ }
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+
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+ return 0;
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}
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#endif
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@@ -94,7 +109,12 @@ tdep_init_mem_validate (void)
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{
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#ifdef HAVE_MINCORE
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unsigned char present = 1;
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- if (mincore (&present, 1, &present) == 0)
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+ unw_word_t addr = PAGE_START((unw_word_t)&present);
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+ unsigned char mvec[1];
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+ int ret;
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+ while ((ret = mincore ((void*)addr, PAGE_SIZE, mvec)) == -1 &&
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+ errno == EAGAIN) {}
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+ if (ret == 0 && (mvec[0] & 1))
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{
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Debug(1, "using mincore to validate memory\n");
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mem_validate_func = mincore_validate;
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--
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cgit v1.0
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