From 7ff9ff039380008952c6fd32011dd2a4d5666906 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Wed, 3 Jan 2024 12:34:14 +0000 Subject: [PATCH] meson: mitigate against use of uninitialize stack for exploits MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When variables are used without being initialized, there is potential to take advantage of data that was pre-existing on the stack from an earlier call, to drive an exploit. It is good practice to always initialize variables, and the compiler can warn about flaws when -Wuninitialized is present. This warning, however, is by no means foolproof with its output varying depending on compiler version and which optimizations are enabled. The -ftrivial-auto-var-init option can be used to tell the compiler to always initialize all variables. This increases the security and predictability of the program, closing off certain attack vectors, reducing the risk of unsafe memory disclosure. While the option takes several possible values, using 'zero' is considered to be the option that is likely to lead to semantically correct or safe behaviour[1]. eg sizes/indexes are not likely to lead to out-of-bounds accesses when initialized to zero. Pointers are less likely to point something useful if initialized to zero. Even with -ftrivial-auto-var-init=zero set, GCC will still issue warnings with -Wuninitialized if it discovers a problem, so we are not loosing diagnostics for developers, just hardening runtime behaviour and making QEMU behave more predictably in case of hitting bad codepaths. [1] https://lists.llvm.org/pipermail/cfe-dev/2020-April/065221.html Signed-off-by: "Daniel P. Berrangé" Message-ID: <20240103123414.2401208-3-berrange@redhat.com> Signed-off-by: Thomas Huth --- meson.build | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/meson.build b/meson.build index 1bda391de6..d0329966f1 100644 --- a/meson.build +++ b/meson.build @@ -559,6 +559,11 @@ hardening_flags = [ # upon its return. This makes it harder to assemble # ROP gadgets into something usable '-fzero-call-used-regs=used-gpr', + + # Initialize all stack variables to zero. This makes + # it harder to take advantage of uninitialized stack + # data to drive exploits + '-ftrivial-auto-var-init=zero', ] qemu_common_flags += cc.get_supported_arguments(hardening_flags)