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Peter Anvin" , Peter Zijlstra , Qi Zheng , Alexandre Ghiti , Josh Poimboeuf , "Kirill A. Shutemov" , Rick Edgecombe , Brian Gerst , Bjorn Helgaas , Tony Battersby , linux-kernel@vger.kernel.org, x86@kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH 2/2] binfmt_elf: Leave a gap between .bss and brk Date: Fri, 16 Feb 2024 22:25:44 -0800 Message-Id: <20240217062545.1631668-2-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240217062035.work.493-kees@kernel.org> References: <20240217062035.work.493-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1512; i=keescook@chromium.org; h=from:subject; bh=Y9GWQSNdeMe/TiCQJCjXENrVrfi7E3amSjOSWzM2S1o=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBl0FFoSMLWKnRZV/Xpg3nYIyPCuv0NWoUMuFI3f ssQMNwOx8mJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZdBRaAAKCRCJcvTf3G3A JvXFD/0ZGY+pv/RW0jEwUr/fOJKrMeYvRA+q8dAhwBU4yZf/9WvOK1OItaQt6erwqczIQcGDsKX RWFEhlQbXwgzOXrwCvEVU3X/MwTvOZFnZ0wTXOJZIuqX6uhvJuDZYq+kDfDixzSf+vvZ5N5gZBO TJzXBbBFV7TqO+okj4IS3xOJWZewgGjhNT8vbeQcPdzj69HDDkXXfpLkoSfygpZcWqlp9XDZiNy vXK3r7lesiRP3IhhoJj7l67XzCYktFTMcgxwx7uHCkePYddv5NSQpYuV1e3GrWYPneqbU/ta/RX cWwsnNmxh2abzRU47UKh05W/uYImIbey5l0CSZI/7QN6m152TAREIrmIXwl2k22fjZgwgd+Apv8 4oW4U/bqzoG9w1PMnHKDMQ9jsdEQB9hjMCKn8XCd+7Gv1wyNPPDXV5RFfLYuFJeaPMBdmXP7zFy E345+0/LhEK6UZl9XBsjpHxXtro8hrLNXyQJNR0dzipAEXd7VeizjMBrL4dibLwpq9Vt5GEwcbV rdHrk6W8yGkeyTm7dflKIXZxINWwAC8JEcnyTOaMiaSf+7Trt7zTSHdjJwqs75llY8Q2hwdTTG3 H4HQ8+CnaTwekWZMYV2AJy4oOxU2TWbO/56rrPwpm2xEE837qZM9Jz9EeaTLbA9t0NKKZotRk7n IeAJGDC3TTWSd+A== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Currently the brk starts its randomization immediately after .bss, which means there is a chance that when the random offset is 0, linear overflows from .bss can reach into the brk area. Leave at least a single page gap between .bss and brk (when it has not already been explicitly relocated into the mmap range). Reported-by: y0un9n132@gmail.com Closes: https://lore.kernel.org/linux-hardening/CA+2EKTVLvc8hDZc+2Yhwmus=dzOUG5E4gV7ayCbu0MPJTZzWkw@mail.gmail.com/ Signed-off-by: Kees Cook --- Cc: Jiri Kosina Cc: Geert Uytterhoeven Cc: Alexander Viro Cc: Christian Brauner Cc: Jan Kara Cc: Eric Biederman Cc: Christophe Leroy Cc: linux-fsdevel@vger.kernel.org Cc: linux-mm@kvack.org --- fs/binfmt_elf.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 5397b552fbeb..7862962f7a85 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -1262,6 +1262,9 @@ static int load_elf_binary(struct linux_binprm *bprm) if (IS_ENABLED(CONFIG_ARCH_HAS_ELF_RANDOMIZE) && elf_ex->e_type == ET_DYN && !interpreter) { mm->brk = mm->start_brk = ELF_ET_DYN_BASE; + } else { + /* Otherwise leave a gap between .bss and brk. */ + mm->brk = mm->start_brk = mm->brk + PAGE_SIZE; } mm->brk = mm->start_brk = arch_randomize_brk(mm);