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authorAndrey Konovalov <andreyknvl@google.com>2018-12-28 00:30:54 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2018-12-28 12:11:44 -0800
commit41eea9cd239c5b3fff726894f85c97f60e5799a3 (patch)
tree1a22d8495f8f69d9baa8916d347e50178dc00a6c /arch
parent7f94ffbc4c6a1bdb51d39965e4f2acaa19bd798f (diff)
downloadlinux-41eea9cd239c5b3fff726894f85c97f60e5799a3.tar.gz
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. Link: http://lkml.kernel.org/r/c91fe7684070e34dc34b419e6b69498f4dcacc2d.1544099024.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov <andreyknvl@google.com> Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Reviewed-by: Dmitry Vyukov <dvyukov@google.com> Acked-by: Will Deacon <will.deacon@arm.com> Cc: Christoph Lameter <cl@linux.com> Cc: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/arm64/include/asm/brk-imm.h2
-rw-r--r--arch/arm64/kernel/traps.c60
2 files changed, 62 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/brk-imm.h b/arch/arm64/include/asm/brk-imm.h
index ed693c5bcec0..2945fe6cd863 100644
--- a/arch/arm64/include/asm/brk-imm.h
+++ b/arch/arm64/include/asm/brk-imm.h
@@ -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 KGDB_COMPILED_DBG_BRK_IMM 0x401
#define BUG_BRK_IMM 0x800
+#define KASAN_BRK_IMM 0x900
#endif
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 5f4d9acb32f5..cdc71cf70aad 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -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,
};
+#ifdef CONFIG_KASAN_SW_TAGS
+
+#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))
+ return DBG_HOOK_ERROR;
+
+ 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);
+ return DBG_HOOK_HANDLED;
+}
+
+#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,
+};
+#endif
+
/*
* 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)
{
+#ifdef CONFIG_KASAN_SW_TAGS
+ if ((esr & KASAN_ESR_MASK) == KASAN_ESR_VAL)
+ return kasan_handler(regs, esr) != DBG_HOOK_HANDLED;
+#endif
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)
{
register_break_hook(&bug_break_hook);
+#ifdef CONFIG_KASAN_SW_TAGS
+ register_break_hook(&kasan_break_hook);
+#endif
}