perf_regs.c

  1// SPDX-License-Identifier: GPL-2.0
  2#include <linux/compat.h>
  3#include <linux/errno.h>
  4#include <linux/kernel.h>
  5#include <linux/perf_event.h>
  6#include <linux/bug.h>
  7#include <linux/sched/task_stack.h>
  8
  9#include <asm/perf_regs.h>
 10#include <asm/ptrace.h>
 11
 12static u64 perf_ext_regs_value(int idx)
 13{
 14	switch (idx) {
 15	case PERF_REG_ARM64_VG:
 16		if (WARN_ON_ONCE(!system_supports_sve()))
 17			return 0;
 18
 19		/*
 20		 * Vector granule is current length in bits of SVE registers
 21		 * divided by 64.
 22		 */
 23		return (task_get_sve_vl(current) * 8) / 64;
 24	default:
 25		WARN_ON_ONCE(true);
 26		return 0;
 27	}
 28}
 29
 30u64 perf_reg_value(struct pt_regs *regs, int idx)
 31{
 32	if (WARN_ON_ONCE((u32)idx >= PERF_REG_ARM64_EXTENDED_MAX))
 33		return 0;
 34
 35	/*
 36	 * Our handling of compat tasks (PERF_SAMPLE_REGS_ABI_32) is weird, but
 37	 * we're stuck with it for ABI compatibility reasons.
 38	 *
 39	 * For a 32-bit consumer inspecting a 32-bit task, then it will look at
 40	 * the first 16 registers (see arch/arm/include/uapi/asm/perf_regs.h).
 41	 * These correspond directly to a prefix of the registers saved in our
 42	 * 'struct pt_regs', with the exception of the PC, so we copy that down
 43	 * (x15 corresponds to SP_hyp in the architecture).
 44	 *
 45	 * So far, so good.
 46	 *
 47	 * The oddity arises when a 64-bit consumer looks at a 32-bit task and
 48	 * asks for registers beyond PERF_REG_ARM_MAX. In this case, we return
 49	 * SP_usr, LR_usr and PC in the positions where the AArch64 SP, LR and
 50	 * PC registers would normally live. The initial idea was to allow a
 51	 * 64-bit unwinder to unwind a 32-bit task and, although it's not clear
 52	 * how well that works in practice, somebody might be relying on it.
 53	 *
 54	 * At the time we make a sample, we don't know whether the consumer is
 55	 * 32-bit or 64-bit, so we have to cater for both possibilities.
 56	 */
 57	if (compat_user_mode(regs)) {
 58		if ((u32)idx == PERF_REG_ARM64_SP)
 59			return regs->compat_sp;
 60		if ((u32)idx == PERF_REG_ARM64_LR)
 61			return regs->compat_lr;
 62		if (idx == 15)
 63			return regs->pc;
 64	}
 65
 66	if ((u32)idx == PERF_REG_ARM64_SP)
 67		return regs->sp;
 68
 69	if ((u32)idx == PERF_REG_ARM64_PC)
 70		return regs->pc;
 71
 72	if ((u32)idx >= PERF_REG_ARM64_MAX)
 73		return perf_ext_regs_value(idx);
 74
 75	return regs->regs[idx];
 76}
 77
 78#define REG_RESERVED (~((1ULL << PERF_REG_ARM64_MAX) - 1))
 79
 80int perf_reg_validate(u64 mask)
 81{
 82	u64 reserved_mask = REG_RESERVED;
 83
 84	if (system_supports_sve())
 85		reserved_mask &= ~(1ULL << PERF_REG_ARM64_VG);
 86
 87	if (!mask || mask & reserved_mask)
 88		return -EINVAL;
 89
 90	return 0;
 91}
 92
 93u64 perf_reg_abi(struct task_struct *task)
 94{
 95	if (is_compat_thread(task_thread_info(task)))
 96		return PERF_SAMPLE_REGS_ABI_32;
 97	else
 98		return PERF_SAMPLE_REGS_ABI_64;
 99}
100
101void perf_get_regs_user(struct perf_regs *regs_user,
102			struct pt_regs *regs)
103{
104	regs_user->regs = task_pt_regs(current);
105	regs_user->abi = perf_reg_abi(current);
106}