Commit 41eea9cd authored by Andrey Konovalov's avatar Andrey Konovalov Committed by Linus Torvalds
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kasan, arm64: add brk handler for inline instrumentation

Tag-based KASAN inline instrumentation mode (which embeds checks of shadow
memory into the generated code, instead of inserting a callback) generates
a brk instruction when a tag mismatch is detected.

This commit adds a tag-based KASAN specific brk handler, that decodes the
immediate value passed to the brk instructions (to extract information
about the memory access that triggered the mismatch), reads the register
values (x0 contains the guilty address) and reports the bug.


Signed-off-by: default avatarAndrey Konovalov <>
Reviewed-by: default avatarAndrey Ryabinin <>
Reviewed-by: default avatarDmitry Vyukov <>
Acked-by: default avatarWill Deacon <>
Cc: Christoph Lameter <>
Cc: Mark Rutland <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 7f94ffbc
......@@ -16,10 +16,12 @@
* 0x400: for dynamic BRK instruction
* 0x401: for compile time BRK instruction
* 0x800: kernel-mode BUG() and WARN() traps
* 0x9xx: tag-based KASAN trap (allowed values 0x900 - 0x9ff)
#define FAULT_BRK_IMM 0x100
#define KGDB_DYN_DBG_BRK_IMM 0x400
#define BUG_BRK_IMM 0x800
#define KASAN_BRK_IMM 0x900
......@@ -35,6 +35,7 @@
#include <linux/sizes.h>
#include <linux/syscalls.h>
#include <linux/mm_types.h>
#include <linux/kasan.h>
#include <asm/atomic.h>
#include <asm/bug.h>
......@@ -969,6 +970,58 @@ static struct break_hook bug_break_hook = {
.fn = bug_handler,
#define KASAN_ESR_RECOVER 0x20
#define KASAN_ESR_WRITE 0x10
#define KASAN_ESR_SIZE_MASK 0x0f
#define KASAN_ESR_SIZE(esr) (1 << ((esr) & KASAN_ESR_SIZE_MASK))
static int kasan_handler(struct pt_regs *regs, unsigned int esr)
bool recover = esr & KASAN_ESR_RECOVER;
bool write = esr & KASAN_ESR_WRITE;
size_t size = KASAN_ESR_SIZE(esr);
u64 addr = regs->regs[0];
u64 pc = regs->pc;
if (user_mode(regs))
kasan_report(addr, size, write, pc);
* The instrumentation allows to control whether we can proceed after
* a crash was detected. This is done by passing the -recover flag to
* the compiler. Disabling recovery allows to generate more compact
* code.
* Unfortunately disabling recovery doesn't work for the kernel right
* now. KASAN reporting is disabled in some contexts (for example when
* the allocator accesses slab object metadata; this is controlled by
* current->kasan_depth). All these accesses are detected by the tool,
* even though the reports for them are not printed.
* This is something that might be fixed at some point in the future.
if (!recover)
die("Oops - KASAN", regs, 0);
/* If thread survives, skip over the brk instruction and continue: */
arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
#define KASAN_ESR_VAL (0xf2000000 | KASAN_BRK_IMM)
#define KASAN_ESR_MASK 0xffffff00
static struct break_hook kasan_break_hook = {
.esr_val = KASAN_ESR_VAL,
.esr_mask = KASAN_ESR_MASK,
.fn = kasan_handler,
* Initial handler for AArch64 BRK exceptions
* This handler only used until debug_traps_init().
......@@ -976,6 +1029,10 @@ static struct break_hook bug_break_hook = {
int __init early_brk64(unsigned long addr, unsigned int esr,
struct pt_regs *regs)
return kasan_handler(regs, esr) != DBG_HOOK_HANDLED;
return bug_handler(regs, esr) != DBG_HOOK_HANDLED;
......@@ -983,4 +1040,7 @@ int __init early_brk64(unsigned long addr, unsigned int esr,
void __init trap_init(void)
......@@ -173,6 +173,9 @@ void kasan_init_tags(void);
void *kasan_reset_tag(const void *addr);
void kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip);
static inline void kasan_init_tags(void) { }
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