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[192.33.36.4]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-579cd4c85c7sm3793847a12.20.2024.05.28.10.01.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 May 2024 10:01:27 -0700 (PDT) Date: Tue, 28 May 2024 19:01:25 +0200 From: Brian Johannesmeyer To: Alexander Potapenko Cc: elver@google.com, dvyukov@google.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org Subject: Re: [PATCH 1/2] kmsan: do not wipe out origin when doing partial unpoisoning Message-ID: References: <20240528104807.738758-1-glider@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240528104807.738758-1-glider@google.com> X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 9AC6910003E X-Stat-Signature: rtppkx97bsdexa6os93dtqk5dniiiz1q X-HE-Tag: 1716915689-912003 X-HE-Meta: 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 qpn5ScNf 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000011, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, May 28, 2024 at 12:48:06PM +0200, Alexander Potapenko wrote: > As noticed by Brian, KMSAN should not be zeroing the origin when > unpoisoning parts of a four-byte uninitialized value, e.g.: > > char a[4]; > kmsan_unpoison_memory(a, 1); > > This led to false negatives, as certain poisoned values could receive zero > origins, preventing those values from being reported. > > To fix the problem, check that kmsan_internal_set_shadow_origin() writes > zero origins only to slots which have zero shadow. > > Reported-by: Brian Johannesmeyer > Link: https://lore.kernel.org/lkml/20240524232804.1984355-1-bjohannesmeyer@gmail.com/T/ > Fixes: f80be4571b19 ("kmsan: add KMSAN runtime core") > Signed-off-by: Alexander Potapenko > --- > mm/kmsan/core.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/mm/kmsan/core.c b/mm/kmsan/core.c > index cf2d70e9c9a5f..95f859e38c533 100644 > --- a/mm/kmsan/core.c > +++ b/mm/kmsan/core.c > @@ -196,8 +196,7 @@ void kmsan_internal_set_shadow_origin(void *addr, size_t size, int b, > u32 origin, bool checked) > { > u64 address = (u64)addr; > - void *shadow_start; > - u32 *origin_start; > + u32 *shadow_start, *origin_start; > size_t pad = 0; > > KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size)); > @@ -225,8 +224,16 @@ void kmsan_internal_set_shadow_origin(void *addr, size_t size, int b, > origin_start = > (u32 *)kmsan_get_metadata((void *)address, KMSAN_META_ORIGIN); > > - for (int i = 0; i < size / KMSAN_ORIGIN_SIZE; i++) > - origin_start[i] = origin; > + /* > + * If the new origin is non-zero, assume that the shadow byte is also non-zero, > + * and unconditionally overwrite the old origin slot. > + * If the new origin is zero, overwrite the old origin slot iff the > + * corresponding shadow slot is zero. > + */ > + for (int i = 0; i < size / KMSAN_ORIGIN_SIZE; i++) { > + if (origin || !shadow_start[i]) > + origin_start[i] = origin; > + } > } > > struct page *kmsan_vmalloc_to_page_or_null(void *vaddr) > -- > 2.45.1.288.g0e0cd299f1-goog > Tested-by: Brian Johannesmeyer