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[34.125.32.3]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-24668864426sm136937785ad.80.2025.08.27.21.17.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 Aug 2025 21:17:04 -0700 (PDT) Date: Thu, 28 Aug 2025 04:16:59 +0000 From: Carlos Llamas To: "Liam R. Howlett" Cc: Andrew Morton , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pedro Falcato , kernel-team@android.com, linux-kernel@vger.kernel.org, "open list:MEMORY MAPPING" Subject: Re: [PATCH] mm/mremap: fix regression in vrm->new_addr check Message-ID: References: <20250828032653.521314-1-cmllamas@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Aug 28, 2025 at 04:06:58AM +0000, Carlos Llamas wrote: > On Wed, Aug 27, 2025 at 11:43:39PM -0400, Liam R. Howlett wrote: > > * Carlos Llamas [250827 23:27]: > > > Commit 3215eaceca87 ("mm/mremap: refactor initial parameter sanity > > > checks") moved the sanity check for vrm->new_addr from mremap_to() to > > > check_mremap_params(). > > > > > > However, this caused a regression as vrm->new_addr is now checked even > > > when MREMAP_FIXED and MREMAP_DONTUNMAP flags are not specified. In this > > > case, vrm->new_addr can be garbage and create unexpected failures. > > > > > > Fix this by moving the new_addr check after the vrm_implies_new_addr() > > > guard. This ensures that the new_addr is only checked when the user has > > > specified one explicitly. > > > > > > Fixes: 3215eaceca87 ("mm/mremap: refactor initial parameter sanity checks") > > > Signed-off-by: Carlos Llamas > > > > I assume this showed up with clang? > > Right. > > The specific test that broke on our end was this: > https://android.googlesource.com/platform/bionic/+/HEAD/tests/__cxa_atexit_test.cpp > Although I'm not exactly sure how __cxa_atexit() implementation uses > mremap() underneath. Ok, here is the specific call to mremap() in the test: https://android.googlesource.com/platform/bionic/+/HEAD/libc/bionic/atexit.cpp#197