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arm64: insn: simplify insn group identification

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The only code which needs to check for an entire instruction group is
the aarch64_insn_is_steppable() helper function used by kprobes, which
must not be instrumented, and only needs to check for the "Branch,
exception generation and system instructions" class.

Currently we have an out-of-line helper in insn.c which must be marked
as __kprobes, which indexes a table with some bits extracted from the
instruction. In aarch64_insn_is_steppable() we then need to compare the
result with an expected enum value.

It would be simpler to have a predicate for this, as with the other
aarch64_insn_is_*() helpers, which would be always inlined to prevent
inadvertent instrumentation, and would permit better code generation.

This patch adds a predicate function for this instruction group using
the existing __AARCH64_INSN_FUNCS() helpers, and removes the existing
out-of-line helper. As the only class we currently care about is the
branch+exception+sys class, I have only added helpers for this, and left
the other classes unimplemented for now.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Joey Gouly <joey.gouly@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20221114135928.3000571-4-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Rutland 2022-11-14 13:59:27 +00:00 committed by Will Deacon
parent 9b948e79d5
commit 4488f90c86
3 changed files with 18 additions and 50 deletions
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42
arch/arm64/include/asm/insn.h
View File

@ -13,31 +13,6 @@
#include <asm/insn-def.h>
#ifndef __ASSEMBLY__
/*
* ARM Architecture Reference Manual for ARMv8 Profile-A, Issue A.a
* Section C3.1 "A64 instruction index by encoding":
* AArch64 main encoding table
* Bit position
* 28 27 26 25 Encoding Group
* 0 0 - - Unallocated
* 1 0 0 - Data processing, immediate
* 1 0 1 - Branch, exception generation and system instructions
* - 1 - 0 Loads and stores
* - 1 0 1 Data processing - register
* 0 1 1 1 Data processing - SIMD and floating point
* 1 1 1 1 Data processing - SIMD and floating point
* "-" means "don't care"
*/
enum aarch64_insn_encoding_class {
AARCH64_INSN_CLS_UNKNOWN, /* UNALLOCATED */
AARCH64_INSN_CLS_SVE, /* SVE instructions */
AARCH64_INSN_CLS_DP_IMM, /* Data processing - immediate */
AARCH64_INSN_CLS_DP_REG, /* Data processing - register */
AARCH64_INSN_CLS_DP_FPSIMD, /* Data processing - SIMD and FP */
AARCH64_INSN_CLS_LDST, /* Loads and stores */
AARCH64_INSN_CLS_BR_SYS, /* Branch, exception generation and
* system instructions */
};
enum aarch64_insn_hint_cr_op {
AARCH64_INSN_HINT_NOP = 0x0 << 5,
@ -326,6 +301,23 @@ static __always_inline u32 aarch64_insn_get_##abbr##_value(void) \
return (val); \
}
/*
* ARM Architecture Reference Manual for ARMv8 Profile-A, Issue A.a
* Section C3.1 "A64 instruction index by encoding":
* AArch64 main encoding table
* Bit position
* 28 27 26 25 Encoding Group
* 0 0 - - Unallocated
* 1 0 0 - Data processing, immediate
* 1 0 1 - Branch, exception generation and system instructions
* - 1 - 0 Loads and stores
* - 1 0 1 Data processing - register
* 0 1 1 1 Data processing - SIMD and floating point
* 1 1 1 1 Data processing - SIMD and floating point
* "-" means "don't care"
*/
__AARCH64_INSN_FUNCS(class_branch_sys, 0x1c000000, 0x14000000)
__AARCH64_INSN_FUNCS(adr, 0x9F000000, 0x10000000)
__AARCH64_INSN_FUNCS(adrp, 0x9F000000, 0x90000000)
__AARCH64_INSN_FUNCS(prfm, 0x3FC00000, 0x39800000)

2
arch/arm64/kernel/probes/decode-insn.c
View File

@ -24,7 +24,7 @@ static bool __kprobes aarch64_insn_is_steppable(u32 insn)
* currently safe. Lastly, MSR instructions can do any number of nasty
* things we can't handle during single-stepping.
*/
if (aarch64_get_insn_class(insn) == AARCH64_INSN_CLS_BR_SYS) {
if (aarch64_insn_is_class_branch_sys(insn)) {
if (aarch64_insn_is_branch(insn) ||
aarch64_insn_is_msr_imm(insn) ||
aarch64_insn_is_msr_reg(insn) ||

24
arch/arm64/lib/insn.c
View File

@ -20,30 +20,6 @@
#define AARCH64_INSN_N_BIT BIT(22)
#define AARCH64_INSN_LSL_12 BIT(22)
static const int aarch64_insn_encoding_class[] = {
AARCH64_INSN_CLS_UNKNOWN,
AARCH64_INSN_CLS_UNKNOWN,
AARCH64_INSN_CLS_SVE,
AARCH64_INSN_CLS_UNKNOWN,
AARCH64_INSN_CLS_LDST,
AARCH64_INSN_CLS_DP_REG,
AARCH64_INSN_CLS_LDST,
AARCH64_INSN_CLS_DP_FPSIMD,
AARCH64_INSN_CLS_DP_IMM,
AARCH64_INSN_CLS_DP_IMM,
AARCH64_INSN_CLS_BR_SYS,
AARCH64_INSN_CLS_BR_SYS,
AARCH64_INSN_CLS_LDST,
AARCH64_INSN_CLS_DP_REG,
AARCH64_INSN_CLS_LDST,
AARCH64_INSN_CLS_DP_FPSIMD,
};
enum aarch64_insn_encoding_class __kprobes aarch64_get_insn_class(u32 insn)
{
return aarch64_insn_encoding_class[(insn >> 25) & 0xf];
}
static int __kprobes aarch64_get_imm_shift_mask(enum aarch64_insn_imm_type type,
u32 *maskp, int *shiftp)
{