| Message ID | 20230907130642.245222-1-glider@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/2] kmsan: simplify kmsan_internal_memmove_metadata() | expand |
On Thu, 7 Sept 2023 at 15:06, Alexander Potapenko <glider@google.com> wrote: > > kmsan_internal_memmove_metadata() is the function that implements > copying metadata every time memcpy()/memmove() is called. > Because shadow memory stores 1 byte per each byte of kernel memory, > copying the shadow is trivial and can be done by a single memmove() > call. > Origins, on the other hand, are stored as 4-byte values corresponding > to every aligned 4 bytes of kernel memory. Therefore, if either the > source or the destination of kmsan_internal_memmove_metadata() is > unaligned, the number of origin slots corresponding to the source or > destination may differ: > > 1) memcpy(0xffff888080a00000, 0xffff888080900000, 4) > copies 1 origin slot into 1 origin slot: > > src (0xffff888080900000): xxxx > src origins: o111 > dst (0xffff888080a00000): xxxx > dst origins: o111 > > 2) memcpy(0xffff888080a00001, 0xffff888080900000, 4) > copies 1 origin slot into 2 origin slots: > > src (0xffff888080900000): xxxx > src origins: o111 > dst (0xffff888080a00000): .xxx x... > dst origins: o111 o111 > > 3) memcpy(0xffff888080a00000, 0xffff888080900001, 4) > copies 2 origin slots into 1 origin slot: > > src (0xffff888080900000): .xxx x... > src origins: o111 o222 > dst (0xffff888080a00000): xxxx > dst origins: o111 > (or o222) > > Previously, kmsan_internal_memmove_metadata() tried to solve this > problem by copying min(src_slots, dst_slots) as is and cloning the > missing slot on one of the ends, if needed. > This was error-prone even in the simple cases where 4 bytes were copied, > and did not account for situations where the total number of nonzero > origin slots could have increased by more than one after copying: > > memcpy(0xffff888080a00000, 0xffff888080900002, 8) > > src (0xffff888080900002): ..xx .... xx.. > src origins: o111 0000 o222 > dst (0xffff888080a00000): xx.. ..xx > o111 0000 > (or 0000 o222) > > The new implementation simply copies the shadow byte by byte, and > updates the corresponding origin slot, if the shadow byte is nonzero. > This approach can handle complex cases with mixed initialized and > uninitialized bytes. Similarly to KMSAN inline instrumentation, latter > writes to bytes sharing the same origin slots take precedence. > > Signed-off-by: Alexander Potapenko <glider@google.com> I think this needs a Fixes tag. Also, is this corner case exercised by one of the KMSAN KUnit test cases? Otherwise, Acked-by: Marco Elver <elver@google.com> > --- > mm/kmsan/core.c | 127 ++++++++++++------------------------------------ > 1 file changed, 31 insertions(+), 96 deletions(-) > > diff --git a/mm/kmsan/core.c b/mm/kmsan/core.c > index 3adb4c1d3b193..c19f47af04241 100644 > --- a/mm/kmsan/core.c > +++ b/mm/kmsan/core.c > @@ -83,131 +83,66 @@ depot_stack_handle_t kmsan_save_stack_with_flags(gfp_t flags, > /* Copy the metadata following the memmove() behavior. */ > void kmsan_internal_memmove_metadata(void *dst, void *src, size_t n) > { > + depot_stack_handle_t prev_old_origin = 0, prev_new_origin = 0; > + int i, iter, step, src_off, dst_off, oiter_src, oiter_dst; > depot_stack_handle_t old_origin = 0, new_origin = 0; > - int src_slots, dst_slots, i, iter, step, skip_bits; > depot_stack_handle_t *origin_src, *origin_dst; > - void *shadow_src, *shadow_dst; > - u32 *align_shadow_src, shadow; > + u8 *shadow_src, *shadow_dst; > + u32 *align_shadow_dst; > bool backwards; > > shadow_dst = kmsan_get_metadata(dst, KMSAN_META_SHADOW); > if (!shadow_dst) > return; > KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(dst, n)); > + align_shadow_dst = > + (u32 *)ALIGN_DOWN((u64)shadow_dst, KMSAN_ORIGIN_SIZE); > > shadow_src = kmsan_get_metadata(src, KMSAN_META_SHADOW); > if (!shadow_src) { > - /* > - * @src is untracked: zero out destination shadow, ignore the > - * origins, we're done. > - */ > - __memset(shadow_dst, 0, n); > + /* @src is untracked: mark @dst as initialized. */ > + kmsan_internal_unpoison_memory(dst, n, /*checked*/ false); > return; > } > KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(src, n)); > > - __memmove(shadow_dst, shadow_src, n); > - > origin_dst = kmsan_get_metadata(dst, KMSAN_META_ORIGIN); > origin_src = kmsan_get_metadata(src, KMSAN_META_ORIGIN); > KMSAN_WARN_ON(!origin_dst || !origin_src); > - src_slots = (ALIGN((u64)src + n, KMSAN_ORIGIN_SIZE) - > - ALIGN_DOWN((u64)src, KMSAN_ORIGIN_SIZE)) / > - KMSAN_ORIGIN_SIZE; > - dst_slots = (ALIGN((u64)dst + n, KMSAN_ORIGIN_SIZE) - > - ALIGN_DOWN((u64)dst, KMSAN_ORIGIN_SIZE)) / > - KMSAN_ORIGIN_SIZE; > - KMSAN_WARN_ON((src_slots < 1) || (dst_slots < 1)); > - KMSAN_WARN_ON((src_slots - dst_slots > 1) || > - (dst_slots - src_slots < -1)); > > backwards = dst > src; > - i = backwards ? min(src_slots, dst_slots) - 1 : 0; > - iter = backwards ? -1 : 1; > - > - align_shadow_src = > - (u32 *)ALIGN_DOWN((u64)shadow_src, KMSAN_ORIGIN_SIZE); > - for (step = 0; step < min(src_slots, dst_slots); step++, i += iter) { > - KMSAN_WARN_ON(i < 0); > - shadow = align_shadow_src[i]; > - if (i == 0) { > - /* > - * If @src isn't aligned on KMSAN_ORIGIN_SIZE, don't > - * look at the first @src % KMSAN_ORIGIN_SIZE bytes > - * of the first shadow slot. > - */ > - skip_bits = ((u64)src % KMSAN_ORIGIN_SIZE) * 8; > - shadow = (shadow >> skip_bits) << skip_bits; > + step = backwards ? -1 : 1; > + iter = backwards ? n - 1 : 0; > + src_off = (u64)src % KMSAN_ORIGIN_SIZE; > + dst_off = (u64)dst % KMSAN_ORIGIN_SIZE; > + > + /* Copy shadow bytes one by one, updating the origins if necessary. */ > + for (i = 0; i < n; i++, iter += step) { > + oiter_src = (iter + src_off) / KMSAN_ORIGIN_SIZE; > + oiter_dst = (iter + dst_off) / KMSAN_ORIGIN_SIZE; > + if (!shadow_src[iter]) { > + shadow_dst[iter] = 0; > + if (!align_shadow_dst[oiter_dst]) > + origin_dst[oiter_dst] = 0; > + continue; > } > - if (i == src_slots - 1) { > - /* > - * If @src + n isn't aligned on > - * KMSAN_ORIGIN_SIZE, don't look at the last > - * (@src + n) % KMSAN_ORIGIN_SIZE bytes of the > - * last shadow slot. > - */ > - skip_bits = (((u64)src + n) % KMSAN_ORIGIN_SIZE) * 8; > - shadow = (shadow << skip_bits) >> skip_bits; > - } > - /* > - * Overwrite the origin only if the corresponding > - * shadow is nonempty. > - */ > - if (origin_src[i] && (origin_src[i] != old_origin) && shadow) { > - old_origin = origin_src[i]; > - new_origin = kmsan_internal_chain_origin(old_origin); > + shadow_dst[iter] = shadow_src[iter]; > + old_origin = origin_src[oiter_src]; > + if (old_origin == prev_old_origin) > + new_origin = prev_new_origin; > + else { > /* > * kmsan_internal_chain_origin() may return > * NULL, but we don't want to lose the previous > * origin value. > */ > + new_origin = kmsan_internal_chain_origin(old_origin); > if (!new_origin) > new_origin = old_origin; > } > - if (shadow) > - origin_dst[i] = new_origin; > - else > - origin_dst[i] = 0; > - } > - /* > - * If dst_slots is greater than src_slots (i.e. > - * dst_slots == src_slots + 1), there is an extra origin slot at the > - * beginning or end of the destination buffer, for which we take the > - * origin from the previous slot. > - * This is only done if the part of the source shadow corresponding to > - * slot is non-zero. > - * > - * E.g. if we copy 8 aligned bytes that are marked as uninitialized > - * and have origins o111 and o222, to an unaligned buffer with offset 1, > - * these two origins are copied to three origin slots, so one of then > - * needs to be duplicated, depending on the copy direction (@backwards) > - * > - * src shadow: |uuuu|uuuu|....| > - * src origin: |o111|o222|....| > - * > - * backwards = 0: > - * dst shadow: |.uuu|uuuu|u...| > - * dst origin: |....|o111|o222| - fill the empty slot with o111 > - * backwards = 1: > - * dst shadow: |.uuu|uuuu|u...| > - * dst origin: |o111|o222|....| - fill the empty slot with o222 > - */ > - if (src_slots < dst_slots) { > - if (backwards) { > - shadow = align_shadow_src[src_slots - 1]; > - skip_bits = (((u64)dst + n) % KMSAN_ORIGIN_SIZE) * 8; > - shadow = (shadow << skip_bits) >> skip_bits; > - if (shadow) > - /* src_slots > 0, therefore dst_slots is at least 2 */ > - origin_dst[dst_slots - 1] = > - origin_dst[dst_slots - 2]; > - } else { > - shadow = align_shadow_src[0]; > - skip_bits = ((u64)dst % KMSAN_ORIGIN_SIZE) * 8; > - shadow = (shadow >> skip_bits) << skip_bits; > - if (shadow) > - origin_dst[0] = origin_dst[1]; > - } > + origin_dst[oiter_dst] = new_origin; > + prev_new_origin = new_origin; > + prev_old_origin = old_origin; > } > } > > -- > 2.42.0.283.g2d96d420d3-goog >
On Mon, Sep 11, 2023 at 1:44 PM Marco Elver <elver@google.com> wrote: > > On Thu, 7 Sept 2023 at 15:06, Alexander Potapenko <glider@google.com> wrote: > > > > kmsan_internal_memmove_metadata() is the function that implements > > copying metadata every time memcpy()/memmove() is called. > > Because shadow memory stores 1 byte per each byte of kernel memory, > > copying the shadow is trivial and can be done by a single memmove() > > call. > > Origins, on the other hand, are stored as 4-byte values corresponding > > to every aligned 4 bytes of kernel memory. Therefore, if either the > > source or the destination of kmsan_internal_memmove_metadata() is > > unaligned, the number of origin slots corresponding to the source or > > destination may differ: > > > > 1) memcpy(0xffff888080a00000, 0xffff888080900000, 4) > > copies 1 origin slot into 1 origin slot: > > > > src (0xffff888080900000): xxxx > > src origins: o111 > > dst (0xffff888080a00000): xxxx > > dst origins: o111 > > > > 2) memcpy(0xffff888080a00001, 0xffff888080900000, 4) > > copies 1 origin slot into 2 origin slots: > > > > src (0xffff888080900000): xxxx > > src origins: o111 > > dst (0xffff888080a00000): .xxx x... > > dst origins: o111 o111 > > > > 3) memcpy(0xffff888080a00000, 0xffff888080900001, 4) > > copies 2 origin slots into 1 origin slot: > > > > src (0xffff888080900000): .xxx x... > > src origins: o111 o222 > > dst (0xffff888080a00000): xxxx > > dst origins: o111 > > (or o222) > > > > Previously, kmsan_internal_memmove_metadata() tried to solve this > > problem by copying min(src_slots, dst_slots) as is and cloning the > > missing slot on one of the ends, if needed. > > This was error-prone even in the simple cases where 4 bytes were copied, > > and did not account for situations where the total number of nonzero > > origin slots could have increased by more than one after copying: > > > > memcpy(0xffff888080a00000, 0xffff888080900002, 8) > > > > src (0xffff888080900002): ..xx .... xx.. > > src origins: o111 0000 o222 > > dst (0xffff888080a00000): xx.. ..xx > > o111 0000 > > (or 0000 o222) > > > > The new implementation simply copies the shadow byte by byte, and > > updates the corresponding origin slot, if the shadow byte is nonzero. > > This approach can handle complex cases with mixed initialized and > > uninitialized bytes. Similarly to KMSAN inline instrumentation, latter > > writes to bytes sharing the same origin slots take precedence. > > > > Signed-off-by: Alexander Potapenko <glider@google.com> > > I think this needs a Fixes tag. Thanks, will add in v2! > Also, is this corner case exercised by one of the KMSAN KUnit test cases? Ditto > Otherwise, > > Acked-by: Marco Elver <elver@google.com>
diff --git a/mm/kmsan/core.c b/mm/kmsan/core.c index 3adb4c1d3b193..c19f47af04241 100644 --- a/mm/kmsan/core.c +++ b/mm/kmsan/core.c @@ -83,131 +83,66 @@ depot_stack_handle_t kmsan_save_stack_with_flags(gfp_t flags, /* Copy the metadata following the memmove() behavior. */ void kmsan_internal_memmove_metadata(void *dst, void *src, size_t n) { + depot_stack_handle_t prev_old_origin = 0, prev_new_origin = 0; + int i, iter, step, src_off, dst_off, oiter_src, oiter_dst; depot_stack_handle_t old_origin = 0, new_origin = 0; - int src_slots, dst_slots, i, iter, step, skip_bits; depot_stack_handle_t *origin_src, *origin_dst; - void *shadow_src, *shadow_dst; - u32 *align_shadow_src, shadow; + u8 *shadow_src, *shadow_dst; + u32 *align_shadow_dst; bool backwards; shadow_dst = kmsan_get_metadata(dst, KMSAN_META_SHADOW); if (!shadow_dst) return; KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(dst, n)); + align_shadow_dst = + (u32 *)ALIGN_DOWN((u64)shadow_dst, KMSAN_ORIGIN_SIZE); shadow_src = kmsan_get_metadata(src, KMSAN_META_SHADOW); if (!shadow_src) { - /* - * @src is untracked: zero out destination shadow, ignore the - * origins, we're done. - */ - __memset(shadow_dst, 0, n); + /* @src is untracked: mark @dst as initialized. */ + kmsan_internal_unpoison_memory(dst, n, /*checked*/ false); return; } KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(src, n)); - __memmove(shadow_dst, shadow_src, n); - origin_dst = kmsan_get_metadata(dst, KMSAN_META_ORIGIN); origin_src = kmsan_get_metadata(src, KMSAN_META_ORIGIN); KMSAN_WARN_ON(!origin_dst || !origin_src); - src_slots = (ALIGN((u64)src + n, KMSAN_ORIGIN_SIZE) - - ALIGN_DOWN((u64)src, KMSAN_ORIGIN_SIZE)) / - KMSAN_ORIGIN_SIZE; - dst_slots = (ALIGN((u64)dst + n, KMSAN_ORIGIN_SIZE) - - ALIGN_DOWN((u64)dst, KMSAN_ORIGIN_SIZE)) / - KMSAN_ORIGIN_SIZE; - KMSAN_WARN_ON((src_slots < 1) || (dst_slots < 1)); - KMSAN_WARN_ON((src_slots - dst_slots > 1) || - (dst_slots - src_slots < -1)); backwards = dst > src; - i = backwards ? min(src_slots, dst_slots) - 1 : 0; - iter = backwards ? -1 : 1; - - align_shadow_src = - (u32 *)ALIGN_DOWN((u64)shadow_src, KMSAN_ORIGIN_SIZE); - for (step = 0; step < min(src_slots, dst_slots); step++, i += iter) { - KMSAN_WARN_ON(i < 0); - shadow = align_shadow_src[i]; - if (i == 0) { - /* - * If @src isn't aligned on KMSAN_ORIGIN_SIZE, don't - * look at the first @src % KMSAN_ORIGIN_SIZE bytes - * of the first shadow slot. - */ - skip_bits = ((u64)src % KMSAN_ORIGIN_SIZE) * 8; - shadow = (shadow >> skip_bits) << skip_bits; + step = backwards ? -1 : 1; + iter = backwards ? n - 1 : 0; + src_off = (u64)src % KMSAN_ORIGIN_SIZE; + dst_off = (u64)dst % KMSAN_ORIGIN_SIZE; + + /* Copy shadow bytes one by one, updating the origins if necessary. */ + for (i = 0; i < n; i++, iter += step) { + oiter_src = (iter + src_off) / KMSAN_ORIGIN_SIZE; + oiter_dst = (iter + dst_off) / KMSAN_ORIGIN_SIZE; + if (!shadow_src[iter]) { + shadow_dst[iter] = 0; + if (!align_shadow_dst[oiter_dst]) + origin_dst[oiter_dst] = 0; + continue; } - if (i == src_slots - 1) { - /* - * If @src + n isn't aligned on - * KMSAN_ORIGIN_SIZE, don't look at the last - * (@src + n) % KMSAN_ORIGIN_SIZE bytes of the - * last shadow slot. - */ - skip_bits = (((u64)src + n) % KMSAN_ORIGIN_SIZE) * 8; - shadow = (shadow << skip_bits) >> skip_bits; - } - /* - * Overwrite the origin only if the corresponding - * shadow is nonempty. - */ - if (origin_src[i] && (origin_src[i] != old_origin) && shadow) { - old_origin = origin_src[i]; - new_origin = kmsan_internal_chain_origin(old_origin); + shadow_dst[iter] = shadow_src[iter]; + old_origin = origin_src[oiter_src]; + if (old_origin == prev_old_origin) + new_origin = prev_new_origin; + else { /* * kmsan_internal_chain_origin() may return * NULL, but we don't want to lose the previous * origin value. */ + new_origin = kmsan_internal_chain_origin(old_origin); if (!new_origin) new_origin = old_origin; } - if (shadow) - origin_dst[i] = new_origin; - else - origin_dst[i] = 0; - } - /* - * If dst_slots is greater than src_slots (i.e. - * dst_slots == src_slots + 1), there is an extra origin slot at the - * beginning or end of the destination buffer, for which we take the - * origin from the previous slot. - * This is only done if the part of the source shadow corresponding to - * slot is non-zero. - * - * E.g. if we copy 8 aligned bytes that are marked as uninitialized - * and have origins o111 and o222, to an unaligned buffer with offset 1, - * these two origins are copied to three origin slots, so one of then - * needs to be duplicated, depending on the copy direction (@backwards) - * - * src shadow: |uuuu|uuuu|....| - * src origin: |o111|o222|....| - * - * backwards = 0: - * dst shadow: |.uuu|uuuu|u...| - * dst origin: |....|o111|o222| - fill the empty slot with o111 - * backwards = 1: - * dst shadow: |.uuu|uuuu|u...| - * dst origin: |o111|o222|....| - fill the empty slot with o222 - */ - if (src_slots < dst_slots) { - if (backwards) { - shadow = align_shadow_src[src_slots - 1]; - skip_bits = (((u64)dst + n) % KMSAN_ORIGIN_SIZE) * 8; - shadow = (shadow << skip_bits) >> skip_bits; - if (shadow) - /* src_slots > 0, therefore dst_slots is at least 2 */ - origin_dst[dst_slots - 1] = - origin_dst[dst_slots - 2]; - } else { - shadow = align_shadow_src[0]; - skip_bits = ((u64)dst % KMSAN_ORIGIN_SIZE) * 8; - shadow = (shadow >> skip_bits) << skip_bits; - if (shadow) - origin_dst[0] = origin_dst[1]; - } + origin_dst[oiter_dst] = new_origin; + prev_new_origin = new_origin; + prev_old_origin = old_origin; } }
kmsan_internal_memmove_metadata() is the function that implements copying metadata every time memcpy()/memmove() is called. Because shadow memory stores 1 byte per each byte of kernel memory, copying the shadow is trivial and can be done by a single memmove() call. Origins, on the other hand, are stored as 4-byte values corresponding to every aligned 4 bytes of kernel memory. Therefore, if either the source or the destination of kmsan_internal_memmove_metadata() is unaligned, the number of origin slots corresponding to the source or destination may differ: 1) memcpy(0xffff888080a00000, 0xffff888080900000, 4) copies 1 origin slot into 1 origin slot: src (0xffff888080900000): xxxx src origins: o111 dst (0xffff888080a00000): xxxx dst origins: o111 2) memcpy(0xffff888080a00001, 0xffff888080900000, 4) copies 1 origin slot into 2 origin slots: src (0xffff888080900000): xxxx src origins: o111 dst (0xffff888080a00000): .xxx x... dst origins: o111 o111 3) memcpy(0xffff888080a00000, 0xffff888080900001, 4) copies 2 origin slots into 1 origin slot: src (0xffff888080900000): .xxx x... src origins: o111 o222 dst (0xffff888080a00000): xxxx dst origins: o111 (or o222) Previously, kmsan_internal_memmove_metadata() tried to solve this problem by copying min(src_slots, dst_slots) as is and cloning the missing slot on one of the ends, if needed. This was error-prone even in the simple cases where 4 bytes were copied, and did not account for situations where the total number of nonzero origin slots could have increased by more than one after copying: memcpy(0xffff888080a00000, 0xffff888080900002, 8) src (0xffff888080900002): ..xx .... xx.. src origins: o111 0000 o222 dst (0xffff888080a00000): xx.. ..xx o111 0000 (or 0000 o222) The new implementation simply copies the shadow byte by byte, and updates the corresponding origin slot, if the shadow byte is nonzero. This approach can handle complex cases with mixed initialized and uninitialized bytes. Similarly to KMSAN inline instrumentation, latter writes to bytes sharing the same origin slots take precedence. Signed-off-by: Alexander Potapenko <glider@google.com> --- mm/kmsan/core.c | 127 ++++++++++++------------------------------------ 1 file changed, 31 insertions(+), 96 deletions(-)