From: Dave Martin <Dave.Martin@arm.com> To: Mark Rutland <mark.rutland@arm.com> Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, arnd@arndb.de, jiong.wang@arm.com, marc.zyngier@arm.com, catalin.marinas@arm.com, suzuki.poulose@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, kvmarm@lists.cs.columbia.edu, christoffer.dall@linaro.org Subject: Re: [RFC 7/9] arm64: expose PAC bit positions via ptrace Date: Tue, 25 Jul 2017 13:11:48 +0100 [thread overview] Message-ID: <20170725121145.GB6321@e103592.cambridge.arm.com> (raw) In-Reply-To: <1491232765-32501-8-git-send-email-mark.rutland@arm.com> 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
WARNING: multiple messages have this Message-ID (diff)
From: Dave.Martin@arm.com (Dave Martin) To: linux-arm-kernel@lists.infradead.org Subject: [RFC 7/9] arm64: expose PAC bit positions via ptrace Date: Tue, 25 Jul 2017 13:11:48 +0100 [thread overview] Message-ID: <20170725121145.GB6321@e103592.cambridge.arm.com> (raw) In-Reply-To: <1491232765-32501-8-git-send-email-mark.rutland@arm.com> 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
next prev parent reply other threads:[~2017-07-25 12:11 UTC|newest] Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-04-03 15:19 [RFC 0/9] ARMv8.3 pointer authentication userspace support Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` [RFC 1/9] asm-generic: mm_hooks: allow hooks to be overridden individually Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` [RFC 2/9] arm64: add pointer authentication register bits Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` [RFC 3/9] arm64/cpufeature: add ARMv8.3 id_aa64isar1 bits Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` [RFC 4/9] arm64/cpufeature: detect pointer authentication Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` [RFC 5/9] arm64: Don't trap host pointer auth use to EL2 Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` [RFC 6/9] arm64: add basic pointer authentication support Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` [RFC 7/9] arm64: expose PAC bit positions via ptrace Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-07-25 12:11 ` Dave Martin [this message] 2017-07-25 12:11 ` Dave Martin 2017-07-25 14:59 ` Mark Rutland 2017-07-25 14:59 ` Mark Rutland 2017-07-25 15:06 ` Dave Martin 2017-07-25 15:06 ` Dave Martin 2017-04-03 15:19 ` [RFC 8/9] arm64/kvm: context-switch PAC registers Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-07 15:41 ` Marc Zyngier 2017-04-07 15:41 ` Marc Zyngier 2017-04-03 15:19 ` [RFC 9/9] arm64: docs: document pointer authentication Mark Rutland 2017-04-03 15:19 ` Mark Rutland 2017-04-07 15:09 ` [RFC 0/9] ARMv8.3 pointer authentication userspace support Adam Wallis 2017-04-07 15:09 ` Adam Wallis
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