Commit ec6e822d authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon

arm64: expose user PAC bit positions via ptrace

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 address authentication feature is
enabled. Otherwise, the regset is hidden.
Reviewed-by: default avatarRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarKristina Martsenko <kristina.martsenko@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
[will: Fix to use vabits_user instead of VA_BITS and rename macro]
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 75031975
......@@ -207,6 +207,9 @@ static inline unsigned long kaslr_offset(void)
return kimage_vaddr - KIMAGE_VADDR;
}
/* the actual size of a user virtual address */
extern u64 vabits_user;
/*
* Allow all memory at the discovery stage. We will clip it later.
*/
......
......@@ -2,9 +2,11 @@
#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_PTR_AUTH
......@@ -61,6 +63,12 @@ static inline void ptrauth_keys_switch(struct ptrauth_keys *keys)
__ptrauth_key_install(APGA, keys->apga);
}
/*
* 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_user_pac_mask() GENMASK(54, vabits_user)
#define ptrauth_thread_init_user(tsk) \
do { \
struct task_struct *__ptiu_tsk = (tsk); \
......
......@@ -53,8 +53,6 @@
*/
#define DEFAULT_MAP_WINDOW_64 (UL(1) << VA_BITS)
extern u64 vabits_user;
#define TASK_SIZE_64 (UL(1) << vabits_user)
#ifdef CONFIG_COMPAT
......
......@@ -229,6 +229,13 @@ 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 */
......@@ -46,6 +46,7 @@
#include <asm/debug-monitors.h>
#include <asm/fpsimd.h>
#include <asm/pgtable.h>
#include <asm/pointer_auth.h>
#include <asm/stacktrace.h>
#include <asm/syscall.h>
#include <asm/traps.h>
......@@ -956,6 +957,30 @@ 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_user_pac_mask();
struct user_pac_mask uregs = {
.data_mask = mask,
.insn_mask = mask,
};
if (!system_supports_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,
......@@ -968,6 +993,9 @@ 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[] = {
......@@ -1037,6 +1065,16 @@ 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 = {
......
......@@ -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 */
......
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