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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id q6sm4042454pfh.127.2020.02.26.13.43.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Feb 2020 13:43:18 -0800 (PST) Date: Wed, 26 Feb 2020 13:43:17 -0800 From: Kees Cook To: Mark Brown Cc: Catalin Marinas , Will Deacon , Alexander Viro , Paul Elliott , Peter Zijlstra , Yu-cheng Yu , Amit Kachhap , Vincenzo Frascino , Marc Zyngier , Eugene Syromiatnikov , Szabolcs Nagy , "H . J . Lu " , Andrew Jones , Arnd Bergmann , Jann Horn , Richard Henderson , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Thomas Gleixner , Florian Weimer , Sudakshina Das , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, Dave Martin Subject: Re: [PATCH v7 05/11] arm64: elf: Enable BTI at exec based on ELF program properties Message-ID: <202002261343.1D0FC8DBE@keescook> References: <20200226155714.43937-1-broonie@kernel.org> <20200226155714.43937-6-broonie@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200226155714.43937-6-broonie@kernel.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 26, 2020 at 03:57:08PM +0000, Mark Brown wrote: > From: Dave Martin > > For BTI protection to be as comprehensive as possible, it is > desirable to have BTI enabled from process startup. If this is not > done, the process must use mprotect() to enable BTI for each of its > executable mappings, but this is painful to do in the libc startup > code. It's simpler and more sound to have the kernel do it > instead. > > To this end, detect BTI support in the executable (or ELF > interpreter, as appropriate), via the > NT_GNU_PROGRAM_PROPERTY_TYPE_0 note, and tweak the initial prot > flags for the process' executable pages to include PROT_BTI as > appropriate. > > Signed-off-by: Dave Martin Reviewed-by: Kees Cook -Kees > Signed-off-by: Mark Brown > --- > arch/arm64/Kconfig | 3 +++ > arch/arm64/include/asm/elf.h | 51 ++++++++++++++++++++++++++++++++++++ > arch/arm64/kernel/process.c | 19 ++++++++++++++ > include/uapi/linux/elf.h | 6 +++++ > 4 files changed, 79 insertions(+) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index e37f4f07b990..d65d226a77ec 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -9,6 +9,7 @@ config ARM64 > select ACPI_MCFG if (ACPI && PCI) > select ACPI_SPCR_TABLE if ACPI > select ACPI_PPTT if ACPI > + select ARCH_BINFMT_ELF_STATE > select ARCH_CLOCKSOURCE_DATA > select ARCH_HAS_DEBUG_VIRTUAL > select ARCH_HAS_DEVMEM_IS_ALLOWED > @@ -33,6 +34,7 @@ config ARM64 > select ARCH_HAS_SYSCALL_WRAPPER > select ARCH_HAS_TEARDOWN_DMA_OPS if IOMMU_SUPPORT > select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST > + select ARCH_HAVE_ELF_PROT > select ARCH_HAVE_NMI_SAFE_CMPXCHG > select ARCH_INLINE_READ_LOCK if !PREEMPTION > select ARCH_INLINE_READ_LOCK_BH if !PREEMPTION > @@ -62,6 +64,7 @@ config ARM64 > select ARCH_INLINE_SPIN_UNLOCK_IRQRESTORE if !PREEMPTION > select ARCH_KEEP_MEMBLOCK > select ARCH_USE_CMPXCHG_LOCKREF > + select ARCH_USE_GNU_PROPERTY if BINFMT_ELF > select ARCH_USE_QUEUED_RWLOCKS > select ARCH_USE_QUEUED_SPINLOCKS > select ARCH_SUPPORTS_MEMORY_FAILURE > diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h > index b618017205a3..c72e381fa86d 100644 > --- a/arch/arm64/include/asm/elf.h > +++ b/arch/arm64/include/asm/elf.h > @@ -114,7 +114,11 @@ > > #ifndef __ASSEMBLY__ > > +#include > #include > +#include > +#include > +#include > #include /* for signal_minsigstksz, used by ARCH_DLINFO */ > > typedef unsigned long elf_greg_t; > @@ -224,6 +228,53 @@ extern int aarch32_setup_additional_pages(struct linux_binprm *bprm, > > #endif /* CONFIG_COMPAT */ > > +struct arch_elf_state { > + int flags; > +}; > + > +#define ARM64_ELF_BTI (1 << 0) > + > +#define INIT_ARCH_ELF_STATE { \ > + .flags = 0, \ > +} > + > +static inline int arch_parse_elf_property(u32 type, const void *data, > + size_t datasz, bool compat, > + struct arch_elf_state *arch) > +{ > + /* No known properties for AArch32 yet */ > + if (IS_ENABLED(CONFIG_COMPAT) && compat) > + return 0; > + > + if (type == GNU_PROPERTY_AARCH64_FEATURE_1_AND) { > + const u32 *p = data; > + > + if (datasz != sizeof(*p)) > + return -ENOEXEC; > + > + if (IS_ENABLED(CONFIG_ARM64_BTI) && > + system_supports_bti() && > + (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) > + arch->flags |= ARM64_ELF_BTI; > + } > + > + return 0; > +} > + > +static inline int arch_elf_pt_proc(void *ehdr, void *phdr, > + struct file *f, bool is_interp, > + struct arch_elf_state *state) > +{ > + return 0; > +} > + > +static inline int arch_check_elf(void *ehdr, bool has_interp, > + void *interp_ehdr, > + struct arch_elf_state *state) > +{ > + return 0; > +} > + > #endif /* !__ASSEMBLY__ */ > > #endif > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index 00626057a384..b8e3faa8d406 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -11,6 +11,7 @@ > > #include > #include > +#include > #include > #include > #include > @@ -18,6 +19,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -654,3 +656,20 @@ asmlinkage void __sched arm64_preempt_schedule_irq(void) > if (system_capabilities_finalized()) > preempt_schedule_irq(); > } > + > +#ifdef CONFIG_BINFMT_ELF > +int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state, > + bool has_interp, bool is_interp) > +{ > + if (is_interp != has_interp) > + return prot; > + > + if (!(state->flags & ARM64_ELF_BTI)) > + return prot; > + > + if (prot & PROT_EXEC) > + prot |= PROT_BTI; > + > + return prot; > +} > +#endif > diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h > index 20900f4496b7..c6dd0215482e 100644 > --- a/include/uapi/linux/elf.h > +++ b/include/uapi/linux/elf.h > @@ -448,4 +448,10 @@ typedef struct elf64_note { > Elf64_Word n_type; /* Content type */ > } Elf64_Nhdr; > > +/* .note.gnu.property types for EM_AARCH64: */ > +#define GNU_PROPERTY_AARCH64_FEATURE_1_AND 0xc0000000 > + > +/* Bits for GNU_PROPERTY_AARCH64_FEATURE_1_BTI */ > +#define GNU_PROPERTY_AARCH64_FEATURE_1_BTI (1U << 0) > + > #endif /* _UAPI_LINUX_ELF_H */ > -- > 2.20.1 > -- Kees Cook