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J . Lu" , Yu-cheng Yu , linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, libc-alpha@sourceware.org, Mark Brown , Dave Martin Subject: [PATCH v5 2/4] arm64: Enable BTI for main executable as well as the interpreter Date: Mon, 19 Jul 2021 17:45:34 +0100 Message-Id: <20210719164536.19143-3-broonie@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20210719164536.19143-1-broonie@kernel.org> References: <20210719164536.19143-1-broonie@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3271; h=from:subject; bh=CO++giUYoHXNfg+ZM1q/9xAugE5bMJJQr1XwojyQrKg=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBg9awtaL5taIcuRXN131n30QOb5aon69WBKpFrMP8R NHv0qSmJATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCYPWsLQAKCRAk1otyXVSH0MWMB/ 9DozwfDb3Ukp7lF1mA8M89pvNhCZtoUzvO2dgWfrJILsc/3NiaAI/DVuxuQs/J65X1iMcJ7a95u4la 1GZuZ1Qw5UMWeOu8uSKZn3i9zqopZp8p911btB695cusfSuCRvq22pJ5vxrYuiumdA3R7LCaMQ2hAz +Yoy5pYO+luv4pnogNrq/J7wYmU940IgL55RDypBRtwhVVs+PbU/7tJ//pgPbZkbvVgJEwFhOBDEsf G3d+TR9OTWp0Ifp+kvLAULsrnTy0BoRIHehWZhl5tcyK2sXMXv/B1CMaMArZQieX69o7RWObwi7dvW WtYohV71JPes/5mHmYOGXT1WyPgPPK X-Developer-Key: i=broonie@kernel.org; a=openpgp; fpr=3F2568AAC26998F9E813A1C5C3F436CA30F5D8EB Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org Currently for dynamically linked ELF executables we only enable BTI for the interpreter, expecting the interpreter to do this for the main executable. This is a bit inconsistent since we do map main executable and is causing issues with systemd's MemoryDenyWriteExecute feature which is implemented using a seccomp filter which prevents setting PROT_EXEC on already mapped memory and lacks the context to be able to detect that memory is already mapped with PROT_EXEC. Resolve this by checking the BTI property for the main executable and enabling BTI if it is present when doing the initial mapping. This does mean that we may get more code with BTI enabled if running on a system without BTI support in the dynamic linker, this is expected to be a safe configuration and testing seems to confirm that. It also reduces the flexibility userspace has to disable BTI but it is expected that for cases where there are problems which require BTI to be disabled it is more likely that it will need to be disabled on a system level. Signed-off-by: Mark Brown Reviewed-by: Dave Martin Tested-by: Jeremy Linton --- arch/arm64/include/asm/elf.h | 15 ++++++++++++--- arch/arm64/kernel/process.c | 14 ++------------ 2 files changed, 14 insertions(+), 15 deletions(-) diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h index a488a1329b16..43b10fd04467 100644 --- a/arch/arm64/include/asm/elf.h +++ b/arch/arm64/include/asm/elf.h @@ -253,12 +253,21 @@ struct arch_elf_state { int flags; }; -#define ARM64_ELF_BTI (1 << 0) +#define ARM64_ELF_INTERP_BTI (1 << 0) +#define ARM64_ELF_EXEC_BTI (1 << 1) #define INIT_ARCH_ELF_STATE { \ .flags = 0, \ } +static inline int arm64_elf_bti_flag(bool is_interp) +{ + if (is_interp) + return ARM64_ELF_INTERP_BTI; + else + return ARM64_ELF_EXEC_BTI; +} + static inline int arch_parse_elf_property(u32 type, const void *data, size_t datasz, bool compat, bool has_interp, bool is_interp, @@ -274,9 +283,9 @@ static inline int arch_parse_elf_property(u32 type, const void *data, if (datasz != sizeof(*p)) return -ENOEXEC; - if (system_supports_bti() && has_interp == is_interp && + if (system_supports_bti() && (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) - arch->flags |= ARM64_ELF_BTI; + arch->flags |= arm64_elf_bti_flag(is_interp); } return 0; diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index c8989b999250..2645bc79b35e 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -686,18 +686,8 @@ core_initcall(tagged_addr_init); int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state, bool has_interp, bool is_interp) { - /* - * For dynamically linked executables the interpreter is - * responsible for setting PROT_BTI on everything except - * itself. - */ - if (is_interp != has_interp) - return prot; - - if (!(state->flags & ARM64_ELF_BTI)) - return prot; - - if (prot & PROT_EXEC) + if ((prot & PROT_EXEC) && + (state->flags & arm64_elf_bti_flag(is_interp))) prot |= PROT_BTI; return prot; -- 2.20.1