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R. Silva" , Bill Wendling , Justin Stitt , linux-kernel@vger.kernel.org Subject: Re: [PATCH 33/82] mm/vmalloc: Refactor intentional wrap-around calculation Message-ID: <202401301356.4F87B727@keescook> References: <20240122235208.work.748-kees@kernel.org> <20240123002814.1396804-33-keescook@chromium.org> <24526e13-2df6-47ea-865f-b5a5594bc024@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 2DA524000E X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: qijmr5g1bzecuh333ueb1zwpoiwzn4xm X-HE-Tag: 1706651833-659705 X-HE-Meta: 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 jASc2Vmv 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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, Jan 30, 2024 at 08:54:00PM +0100, Uladzislau Rezki wrote: > On Tue, Jan 30, 2024 at 06:55:57PM +0000, Lorenzo Stoakes wrote: > > On Mon, Jan 22, 2024 at 04:27:08PM -0800, Kees Cook wrote: > > > In an effort to separate intentional arithmetic wrap-around from > > > unexpected wrap-around, we need to refactor places that depend on this > > > kind of math. One of the most common code patterns of this is: > > > > > > VAR + value < VAR > > > > > > Notably, this is considered "undefined behavior" for signed and pointer > > > types, which the kernel works around by using the -fno-strict-overflow > > > option in the build[1] (which used to just be -fwrapv). Regardless, we > > > want to get the kernel source to the position where we can meaningfully > > > instrument arithmetic wrap-around conditions and catch them when they > > > are unexpected, regardless of whether they are signed[2], unsigned[3], > > > or pointer[4] types. > > > > > > Refactor open-coded unsigned wrap-around addition test to use > > > check_add_overflow(), retaining the result for later usage (which removes > > > the redundant open-coded addition). This paves the way to enabling the > > > unsigned wrap-around sanitizer[2] in the future. > > > > > > Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1] > > > Link: https://github.com/KSPP/linux/issues/26 [2] > > > Link: https://github.com/KSPP/linux/issues/27 [3] > > > Link: https://github.com/KSPP/linux/issues/344 [4] > > > Cc: Andrew Morton > > > Cc: Uladzislau Rezki > > > Cc: Christoph Hellwig > > > Cc: Lorenzo Stoakes > > > Cc: linux-mm@kvack.org > > > Signed-off-by: Kees Cook > > > --- > > > mm/vmalloc.c | 5 +++-- > > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > index d12a17fc0c17..7932ac99e9d3 100644 > > > --- a/mm/vmalloc.c > > > +++ b/mm/vmalloc.c > > > @@ -1223,6 +1223,7 @@ is_within_this_va(struct vmap_area *va, unsigned long size, > > > unsigned long align, unsigned long vstart) > > > { > > > unsigned long nva_start_addr; > > > + unsigned long sum; > > > > > > if (va->va_start > vstart) > > > nva_start_addr = ALIGN(va->va_start, align); > > > @@ -1230,11 +1231,11 @@ is_within_this_va(struct vmap_area *va, unsigned long size, > > > nva_start_addr = ALIGN(vstart, align); > > > > > > /* Can be overflowed due to big size or alignment. */ > > > - if (nva_start_addr + size < nva_start_addr || > > > + if (check_add_overflow(nva_start_addr, size, &sum) || > > > nva_start_addr < vstart) > > > return false; > > > > > > - return (nva_start_addr + size <= va->va_end); > > > + return (sum <= va->va_end); > > > } > > > > > > /* > > > -- > > > 2.34.1 > > > > > > > Looks good to me, > > > > Reviewed-by: Lorenzo Stoakes > > > Same here. One small nit though. The "sum" variable is not something > that it suits for. IMO, we should use a better name and replace it: > > "nva_offset"? Sure, I can use that. Other folks in other patches have suggested "end", so maybe nva_end or nva_end_addr ? -Kees -- Kees Cook