From 8f424750baaafcef229791882e879da01c9473b5 Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Mon, 14 Dec 2020 19:13:41 -0800 Subject: [PATCH] mm, page_poison: remove CONFIG_PAGE_POISONING_NO_SANITY CONFIG_PAGE_POISONING_NO_SANITY skips the check on page alloc whether the poison pattern was corrupted, suggesting a use-after-free. The motivation to introduce it in commit 8823b1dbc05f ("mm/page_poison.c: enable PAGE_POISONING as a separate option") was to simply sanitize freed pages, optimally together with CONFIG_PAGE_POISONING_ZERO. These days we have an init_on_free=1 boot option, which makes this use case of page poisoning redundant. For sanitizing, writing zeroes is sufficient, there is pretty much no benefit from writing the 0xAA poison pattern to freed pages, without checking it back on alloc. Thus, remove this option and suggest init_on_free instead in the main config's help. Link: https://lkml.kernel.org/r/20201113104033.22907-5-vbabka@suse.cz Signed-off-by: Vlastimil Babka Acked-by: David Hildenbrand Cc: Mike Rapoport Cc: Rafael J. Wysocki Cc: Alexander Potapenko Cc: Kees Cook Cc: Laura Abbott Cc: Mateusz Nosek Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/virtio/virtio_balloon.c | 4 +--- mm/Kconfig.debug | 15 ++++----------- mm/page_poison.c | 3 --- 3 files changed, 5 insertions(+), 17 deletions(-) diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index e53faed..8985fc2 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -1114,9 +1114,7 @@ static int virtballoon_validate(struct virtio_device *vdev) * page reporting as it could potentially change the contents * of our free pages. */ - if (!want_init_on_free() && - (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY) || - !page_poisoning_enabled_static())) + if (!want_init_on_free() && !page_poisoning_enabled_static()) __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_PAGE_POISON); else if (!virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) __virtio_clear_bit(vdev, VIRTIO_BALLOON_F_REPORTING); diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug index c57786a..14e29fe 100644 --- a/mm/Kconfig.debug +++ b/mm/Kconfig.debug @@ -74,18 +74,11 @@ config PAGE_POISONING Note that "poison" here is not the same thing as the "HWPoison" for CONFIG_MEMORY_FAILURE. This is software poisoning only. - If unsure, say N + If you are only interested in sanitization of freed pages without + checking the poison pattern on alloc, you can boot the kernel with + "init_on_free=1" instead of enabling this. -config PAGE_POISONING_NO_SANITY - depends on PAGE_POISONING - bool "Only poison, don't sanity check" - help - Skip the sanity checking on alloc, only fill the pages with - poison on free. This reduces some of the overhead of the - poisoning feature. - - If you are only interested in sanitization, say Y. Otherwise - say N. + If unsure, say N config PAGE_POISONING_ZERO bool "Use zero for poisoning instead of debugging value" diff --git a/mm/page_poison.c b/mm/page_poison.c index 4d75fc9..06ec518 100644 --- a/mm/page_poison.c +++ b/mm/page_poison.c @@ -51,9 +51,6 @@ static void check_poison_mem(unsigned char *mem, size_t bytes) unsigned char *start; unsigned char *end; - if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY)) - return; - start = memchr_inv(mem, PAGE_POISON, bytes); if (!start) return; -- 2.7.4