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@xxxxxxx> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > Cc: Jiong Wang <jiong.wang@xxxxxxx> > Cc: Will Deacon <will.deacon@xxxxxxx> > --- > 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
