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Poulose" , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v5 08/17] arm64: expose user PAC bit positions via ptrace Date: Fri, 5 Oct 2018 09:47:45 +0100 Message-Id: <20181005084754.20950-9-kristina.martsenko@arm.com> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20181005084754.20950-1-kristina.martsenko@arm.com> References: <20181005084754.20950-1-kristina.martsenko@arm.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Mark Rutland When pointer authentication is in use, data/instruction pointers have a number of PAC bits inserted into them. The number and position of these bits depends on the configured TCR_ELx.TxSZ and whether tagging is enabled. ARMv8.3 allows tagging to differ for instruction and data pointers. For userspace debuggers to unwind the stack and/or to follow pointer chains, they need to be able to remove the PAC bits before attempting to use a pointer. This patch adds a new structure with masks describing the location of the PAC bits in userspace instruction and data pointers (i.e. those addressable via TTBR0), which userspace can query via PTRACE_GETREGSET. By clearing these bits from pointers (and replacing them with the value of bit 55), userspace can acquire the PAC-less versions. This new regset is exposed when the kernel is built with (user) pointer authentication support, and the feature is enabled. Otherwise, it is hidden. Signed-off-by: Mark Rutland [kristina: cpus_have_cap -> cpus_have_const_cap] Signed-off-by: Kristina Martsenko Cc: Catalin Marinas Cc: Ramana Radhakrishnan Cc: Will Deacon --- arch/arm64/include/asm/pointer_auth.h | 8 ++++++++ arch/arm64/include/uapi/asm/ptrace.h | 7 +++++++ arch/arm64/kernel/ptrace.c | 38 +++++++++++++++++++++++++++++++++++ include/uapi/linux/elf.h | 1 + 4 files changed, 54 insertions(+) diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h index 2aefedc31d9e..15486079e9ec 100644 --- a/arch/arm64/include/asm/pointer_auth.h +++ b/arch/arm64/include/asm/pointer_auth.h @@ -2,9 +2,11 @@ #ifndef __ASM_POINTER_AUTH_H #define __ASM_POINTER_AUTH_H +#include #include #include +#include #include #ifdef CONFIG_ARM64_PTR_AUTH @@ -49,6 +51,12 @@ static inline void ptrauth_keys_switch(struct ptrauth_keys *keys) __ptrauth_key_install(APIA, keys->apia); } +/* + * The EL0 pointer bits used by a pointer authentication code. + * This is dependent on TBI0 being enabled, or bits 63:56 would also apply. + */ +#define ptrauth_pac_mask() GENMASK(54, VA_BITS) + #define mm_ctx_ptrauth_init(ctx) \ ptrauth_keys_init(&(ctx)->ptrauth_keys) diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h index 98c4ce55d9c3..4994d718771a 100644 --- a/arch/arm64/include/uapi/asm/ptrace.h +++ b/arch/arm64/include/uapi/asm/ptrace.h @@ -228,6 +228,13 @@ struct user_sve_header { SVE_PT_SVE_OFFSET + SVE_PT_SVE_SIZE(vq, flags) \ : SVE_PT_FPSIMD_OFFSET + SVE_PT_FPSIMD_SIZE(vq, flags)) +/* pointer authentication masks (NT_ARM_PAC_MASK) */ + +struct user_pac_mask { + __u64 data_mask; + __u64 insn_mask; +}; + #endif /* __ASSEMBLY__ */ #endif /* _UAPI__ASM_PTRACE_H */ diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index 6219486fa25f..cb8246f8c603 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -46,6 +46,7 @@ #include #include #include +#include #include #include #include @@ -958,6 +959,30 @@ static int sve_set(struct task_struct *target, #endif /* CONFIG_ARM64_SVE */ +#ifdef CONFIG_ARM64_PTR_AUTH +static int pac_mask_get(struct task_struct *target, + const struct user_regset *regset, + unsigned int pos, unsigned int count, + void *kbuf, void __user *ubuf) +{ + /* + * The PAC bits can differ across data and instruction pointers + * depending on TCR_EL1.TBID*, which we may make use of in future, so + * we expose separate masks. + */ + unsigned long mask = ptrauth_pac_mask(); + struct user_pac_mask uregs = { + .data_mask = mask, + .insn_mask = mask, + }; + + if (!cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH)) + return -EINVAL; + + return user_regset_copyout(&pos, &count, &kbuf, &ubuf, &uregs, 0, -1); +} +#endif /* CONFIG_ARM64_PTR_AUTH */ + enum aarch64_regset { REGSET_GPR, REGSET_FPR, @@ -970,6 +995,9 @@ enum aarch64_regset { #ifdef CONFIG_ARM64_SVE REGSET_SVE, #endif +#ifdef CONFIG_ARM64_PTR_AUTH + REGSET_PAC_MASK, +#endif }; static const struct user_regset aarch64_regsets[] = { @@ -1039,6 +1067,16 @@ static const struct user_regset aarch64_regsets[] = { .get_size = sve_get_size, }, #endif +#ifdef CONFIG_ARM64_PTR_AUTH + [REGSET_PAC_MASK] = { + .core_note_type = NT_ARM_PAC_MASK, + .n = sizeof(struct user_pac_mask) / sizeof(u64), + .size = sizeof(u64), + .align = sizeof(u64), + .get = pac_mask_get, + /* this cannot be set dynamically */ + }, +#endif }; static const struct user_regset_view user_aarch64_view = { diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h index c5358e0ae7c5..3f23273d690c 100644 --- a/include/uapi/linux/elf.h +++ b/include/uapi/linux/elf.h @@ -420,6 +420,7 @@ typedef struct elf64_shdr { #define NT_ARM_HW_WATCH 0x403 /* ARM hardware watchpoint registers */ #define NT_ARM_SYSTEM_CALL 0x404 /* ARM system call number */ #define NT_ARM_SVE 0x405 /* ARM Scalable Vector Extension registers */ +#define NT_ARM_PAC_MASK 0x406 /* ARM pointer authentication code masks */ #define NT_ARC_V2 0x600 /* ARCv2 accumulator/extra registers */ #define NT_VMCOREDD 0x700 /* Vmcore Device Dump Note */ #define NT_MIPS_DSP 0x800 /* MIPS DSP ASE registers */ -- 2.11.0