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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 v1 2/3] arm64: Enable BTI for main executable as well as the interpreter Date: Fri, 4 Jun 2021 12:17:27 +0100 Message-Id: <20210604111728.12052-3-broonie@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20210604111728.12052-1-broonie@kernel.org> References: <20210604111728.12052-1-broonie@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3182; h=from:subject; bh=YIMcXq5zjPTU6TnWkCaebLW4hx7QitAn2BiMS6aUhsU=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBgugvFd6SBiufM2R00KzOUZstotWdq3dPQbkCl/0c/ dJZN8kGJATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCYLoLxQAKCRAk1otyXVSH0MW+B/ 4yqcJtFuYqviGWjfdRvSgY1i8gr0R6YPB1OB/1kItH5G67EBE6Jt9nEIxdnF8L+neLE+CWXb0+cJbz eB1K6ync2IvC83H8huyA+yX/zbtBd9+KraODNo0VsDbOl/2Z4DuVHEZDBSZMn7SapOJ0z26oD3QIlH 4TcH11vjuY8wfCByMnRnERUgPtQ2mWPENyIseZ8jd2kcR91sN9eNpn+w50RE7eZwfMUPhTFBwuCDse eWoB0onQLrPe8+H5QKvYIw4WaA7bzn3o5SBx3CzrafsXUf7EQNSoPpVAH12Ah3Pjvbf2jqs3SZIJHo G5vF+sdFKXBhUHNO3vR1/suuYNhEJm 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 --- arch/arm64/include/asm/elf.h | 14 ++++++++++---- arch/arm64/kernel/process.c | 18 ++++++------------ 2 files changed, 16 insertions(+), 16 deletions(-) diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h index a488a1329b16..9f86dbce2680 100644 --- a/arch/arm64/include/asm/elf.h +++ b/arch/arm64/include/asm/elf.h @@ -253,7 +253,8 @@ 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, \ @@ -274,9 +275,14 @@ 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 && - (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) - arch->flags |= ARM64_ELF_BTI; + if (system_supports_bti() && + (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) { + if (is_interp) { + arch->flags |= ARM64_ELF_INTERP_BTI; + } else { + arch->flags |= ARM64_ELF_EXEC_BTI; + } + } } return 0; diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index b4bb67f17a2c..f7fff4a4c99f 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -744,19 +744,13 @@ asmlinkage void __sched arm64_preempt_schedule_irq(void) 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 (prot & PROT_EXEC) { + if (state->flags & ARM64_ELF_INTERP_BTI && is_interp) + prot |= PROT_BTI; - if (!(state->flags & ARM64_ELF_BTI)) - return prot; - - if (prot & PROT_EXEC) - prot |= PROT_BTI; + if (state->flags & ARM64_ELF_EXEC_BTI && !is_interp) + prot |= PROT_BTI; + } return prot; } -- 2.20.1