| Message ID | 1491232765-32501-8-git-send-email-mark.rutland@arm.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | ARMv8.3 pointer authentication userspace support | expand |
On Mon, Apr 03, 2017 at 04:19:23PM +0100, Mark Rutland wrote: > 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 > PAC bits in instruction and data pointers, which userspace can query via > PTRACE_GETREGSET. By clearing these bits from pointers, 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. > > Note that even if the feature is available and enabled, we cannot > determine whether userspace is making use of the feature, so debuggers > need to cope with this case regardless. > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Jiong Wang <jiong.wang@arm.com> > Cc: Will Deacon <will.deacon@arm.com> > --- > arch/arm64/include/asm/pointer_auth.h | 8 +++++++ > arch/arm64/include/uapi/asm/ptrace.h | 5 +++++ > arch/arm64/kernel/ptrace.c | 39 +++++++++++++++++++++++++++++++++++ > include/uapi/linux/elf.h | 1 + > 4 files changed, 53 insertions(+) > > diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h > index 345df24..ed505fe 100644 > --- a/arch/arm64/include/asm/pointer_auth.h > +++ b/arch/arm64/include/asm/pointer_auth.h > @@ -16,9 +16,11 @@ > #ifndef __ASM_POINTER_AUTH_H > #define __ASM_POINTER_AUTH_H > > +#include <linux/bitops.h> > #include <linux/random.h> > > #include <asm/cpufeature.h> > +#include <asm/memory.h> > #include <asm/sysreg.h> > > #ifdef CONFIG_ARM64_POINTER_AUTHENTICATION > @@ -70,6 +72,12 @@ static inline void ptrauth_keys_dup(struct ptrauth_keys *old, > *new = *old; > } > > +/* > + * The pointer bits used by a pointer authentication code. > + * If we were to use tagged pointers, bits 63:56 would also apply. > + */ > +#define ptrauth_pac_mask() GENMASK(54, VA_BITS) Tagged pointers _are_ enabled for userspace by default, no? [...] > diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h > index b59ee07..cae3d1e 100644 > --- a/include/uapi/linux/elf.h > +++ b/include/uapi/linux/elf.h > @@ -414,6 +414,7 @@ > #define NT_ARM_HW_BREAK 0x402 /* ARM hardware breakpoint registers */ > #define NT_ARM_HW_WATCH 0x403 /* ARM hardware watchpoint registers */ > #define NT_ARM_SYSTEM_CALL 0x404 /* ARM system call number */ > +#define NT_ARM_PAC_MASK 0x405 /* ARM pointer authentication code masks */ The is the value tentatively assigned to NT_ARM_SVE. Cheers ---Dave
On Tue, Jul 25, 2017 at 01:11:48PM +0100, Dave Martin wrote: > On Mon, Apr 03, 2017 at 04:19:23PM +0100, Mark Rutland wrote: > > +/* > > + * The pointer bits used by a pointer authentication code. > > + * If we were to use tagged pointers, bits 63:56 would also apply. > > + */ > > +#define ptrauth_pac_mask() GENMASK(54, VA_BITS) > > Tagged pointers _are_ enabled for userspace by default, no? Yes; I'd meant s/tagged/untagged/. I've corrected this to: /* * The EL0 pointer bits used by a pointer authentication code. * This is dependent on TBI0 being enabled, or bits 63:56 would also apply. */ > > diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h > > index b59ee07..cae3d1e 100644 > > --- a/include/uapi/linux/elf.h > > +++ b/include/uapi/linux/elf.h > > @@ -414,6 +414,7 @@ > > #define NT_ARM_HW_BREAK 0x402 /* ARM hardware breakpoint registers */ > > #define NT_ARM_HW_WATCH 0x403 /* ARM hardware watchpoint registers */ > > #define NT_ARM_SYSTEM_CALL 0x404 /* ARM system call number */ > > +#define NT_ARM_PAC_MASK 0x405 /* ARM pointer authentication code masks */ > > The is the value tentatively assigned to NT_ARM_SVE. I must've generated this patch before I corrected this; my local branch (and kernel.org) have 0x406 here. Sorry about that. Mark.
On Tue, Jul 25, 2017 at 03:59:04PM +0100, Mark Rutland wrote: > On Tue, Jul 25, 2017 at 01:11:48PM +0100, Dave Martin wrote: > > On Mon, Apr 03, 2017 at 04:19:23PM +0100, Mark Rutland wrote: > > > +/* > > > + * The pointer bits used by a pointer authentication code. > > > + * If we were to use tagged pointers, bits 63:56 would also apply. > > > + */ > > > +#define ptrauth_pac_mask() GENMASK(54, VA_BITS) > > > > Tagged pointers _are_ enabled for userspace by default, no? > > Yes; I'd meant s/tagged/untagged/. > > I've corrected this to: > > /* > * The EL0 pointer bits used by a pointer authentication code. > * This is dependent on TBI0 being enabled, or bits 63:56 would also apply. > */ Yes, that's better. If we do enable untagged pointers for userspace at some point though, this is likely to be missed. I don't have a good answer to this. > > > diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h > > > index b59ee07..cae3d1e 100644 > > > --- a/include/uapi/linux/elf.h > > > +++ b/include/uapi/linux/elf.h > > > @@ -414,6 +414,7 @@ > > > #define NT_ARM_HW_BREAK 0x402 /* ARM hardware breakpoint registers */ > > > #define NT_ARM_HW_WATCH 0x403 /* ARM hardware watchpoint registers */ > > > #define NT_ARM_SYSTEM_CALL 0x404 /* ARM system call number */ > > > +#define NT_ARM_PAC_MASK 0x405 /* ARM pointer authentication code masks */ > > > > The is the value tentatively assigned to NT_ARM_SVE. > > I must've generated this patch before I corrected this; my local branch > (and kernel.org) have 0x406 here. > > Sorry about that. Shame, I had a rant about pragmatism prepped and ready ;) Cheers ---Dave
diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h index 345df24..ed505fe 100644 --- a/arch/arm64/include/asm/pointer_auth.h +++ b/arch/arm64/include/asm/pointer_auth.h @@ -16,9 +16,11 @@ #ifndef __ASM_POINTER_AUTH_H #define __ASM_POINTER_AUTH_H +#include <linux/bitops.h> #include <linux/random.h> #include <asm/cpufeature.h> +#include <asm/memory.h> #include <asm/sysreg.h> #ifdef CONFIG_ARM64_POINTER_AUTHENTICATION @@ -70,6 +72,12 @@ static inline void ptrauth_keys_dup(struct ptrauth_keys *old, *new = *old; } +/* + * The pointer bits used by a pointer authentication code. + * If we were to use tagged pointers, 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 d1ff83d..5092fbf 100644 --- a/arch/arm64/include/uapi/asm/ptrace.h +++ b/arch/arm64/include/uapi/asm/ptrace.h @@ -90,6 +90,11 @@ struct user_hwdebug_state { } dbg_regs[16]; }; +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 c142459..b0bcdfb 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -40,8 +40,10 @@ #include <linux/elf.h> #include <asm/compat.h> +#include <asm/cpufeature.h> #include <asm/debug-monitors.h> #include <asm/pgtable.h> +#include <asm/pointer_auth.h> #include <asm/syscall.h> #include <asm/traps.h> #include <asm/system_misc.h> @@ -693,6 +695,30 @@ static int system_call_set(struct task_struct *target, return ret; } +#ifdef CONFIG_ARM64_POINTER_AUTHENTICATION +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) +{ + /* + * While the PAC bits are currently the same for data and instruction + * pointers, this could change if we use TCR_ELx.TBID*. So we expose + * them separately from the outset. + */ + unsigned long mask = ptrauth_pac_mask(); + struct user_pac_mask uregs = { + .data_mask = mask, + .insn_mask = mask, + }; + + if (!cpus_have_cap(ARM64_HAS_ADDRESS_AUTH)) + return -EINVAL; + + return user_regset_copyout(&pos, &count, &kbuf, &ubuf, &uregs, 0, -1); +} +#endif + enum aarch64_regset { REGSET_GPR, REGSET_FPR, @@ -702,6 +728,9 @@ enum aarch64_regset { REGSET_HW_WATCH, #endif REGSET_SYSTEM_CALL, +#ifdef CONFIG_ARM64_POINTER_AUTHENTICATION + REGSET_PAC_MASK, +#endif }; static const struct user_regset aarch64_regsets[] = { @@ -759,6 +788,16 @@ enum aarch64_regset { .get = system_call_get, .set = system_call_set, }, +#ifdef CONFIG_ARM64_POINTER_AUTHENTICATION + [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 b59ee07..cae3d1e 100644 --- a/include/uapi/linux/elf.h +++ b/include/uapi/linux/elf.h @@ -414,6 +414,7 @@ #define NT_ARM_HW_BREAK 0x402 /* ARM hardware breakpoint registers */ #define NT_ARM_HW_WATCH 0x403 /* ARM hardware watchpoint registers */ #define NT_ARM_SYSTEM_CALL 0x404 /* ARM system call number */ +#define NT_ARM_PAC_MASK 0x405 /* ARM pointer authentication code masks */ #define NT_METAG_CBUF 0x500 /* Metag catch buffer registers */ #define NT_METAG_RPIPE 0x501 /* Metag read pipeline state */ #define NT_METAG_TLS 0x502 /* Metag TLS pointer */
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 PAC bits in instruction and data pointers, which userspace can query via PTRACE_GETREGSET. By clearing these bits from pointers, 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. Note that even if the feature is available and enabled, we cannot determine whether userspace is making use of the feature, so debuggers need to cope with this case regardless. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Jiong Wang <jiong.wang@arm.com> Cc: Will Deacon <will.deacon@arm.com> --- arch/arm64/include/asm/pointer_auth.h | 8 +++++++ arch/arm64/include/uapi/asm/ptrace.h | 5 +++++ arch/arm64/kernel/ptrace.c | 39 +++++++++++++++++++++++++++++++++++ include/uapi/linux/elf.h | 1 + 4 files changed, 53 insertions(+) -- 1.9.1