Re: [PATCH 1/8] kasan,x86: Frob kasan_report() in an exception
From: Peter Zijlstra
Date: Fri Mar 01 2019 - 09:46:09 EST
On Thu, Feb 28, 2019 at 04:22:04PM +0100, Dmitry Vyukov wrote:
> On Thu, Feb 28, 2019 at 4:05 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > Because __asan_{load,store}{N,1,2,4,8,16}_noabort() get called from
> > UACCESS context, and kasan_report() is most definitely _NOT_ safe to
> > be called from there, move it into an exception much like BUG/WARN.
> >
> > *compile tested only*
>
>
> Please test it by booting KASAN kernel and then loading module
> produced by CONFIG_TEST_KASAN=y. There are too many subtle aspects to
> rely on "compile tested only", reviewers can't catch all of them
> either.
The below boots and survives test_kasan.
I'll now try that annotation you preferred. But I think this is a pretty
neat hack :-)
---
Subject: kasan,x86: Frob kasan_report() in an exception
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Thu Feb 28 15:52:03 CET 2019
Because __asan_{load,store}{N,1,2,4,8,16}_noabort() get called from
UACCESS context, and kasan_report() is most definitely _NOT_ safe to
be called from there, move it into an exception much like BUg/WARN.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
arch/x86/include/asm/bug.h | 28 ++++++++++++++--------------
arch/x86/include/asm/kasan.h | 17 +++++++++++++++++
include/asm-generic/bug.h | 1 +
include/linux/kasan.h | 12 +++++++++---
lib/bug.c | 9 ++++++++-
mm/kasan/kasan.h | 2 +-
mm/kasan/report.c | 2 +-
7 files changed, 51 insertions(+), 20 deletions(-)
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -30,33 +30,33 @@
#ifdef CONFIG_DEBUG_BUGVERBOSE
-#define _BUG_FLAGS(ins, flags) \
+#define _BUG_FLAGS(ins, flags, ...) \
do { \
asm volatile("1:\t" ins "\n" \
".pushsection __bug_table,\"aw\"\n" \
- "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
- "\t" __BUG_REL(%c0) "\t# bug_entry::file\n" \
- "\t.word %c1" "\t# bug_entry::line\n" \
- "\t.word %c2" "\t# bug_entry::flags\n" \
- "\t.org 2b+%c3\n" \
+ "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
+ "\t" __BUG_REL(%c[file]) "\t# bug_entry::file\n" \
+ "\t.word %c[line]" "\t# bug_entry::line\n" \
+ "\t.word %c[flag]" "\t# bug_entry::flags\n" \
+ "\t.org 2b+%c[size]\n" \
".popsection" \
- : : "i" (__FILE__), "i" (__LINE__), \
- "i" (flags), \
- "i" (sizeof(struct bug_entry))); \
+ : : [file] "i" (__FILE__), [line] "i" (__LINE__), \
+ [flag] "i" (flags), \
+ [size] "i" (sizeof(struct bug_entry)), ##__VA_ARGS__); \
} while (0)
#else /* !CONFIG_DEBUG_BUGVERBOSE */
-#define _BUG_FLAGS(ins, flags) \
+#define _BUG_FLAGS(ins, flags, ...) \
do { \
asm volatile("1:\t" ins "\n" \
".pushsection __bug_table,\"aw\"\n" \
"2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n" \
- "\t.word %c0" "\t# bug_entry::flags\n" \
- "\t.org 2b+%c1\n" \
+ "\t.word %c[flag]" "\t# bug_entry::flags\n" \
+ "\t.org 2b+%c[size]\n" \
".popsection" \
- : : "i" (flags), \
- "i" (sizeof(struct bug_entry))); \
+ : : [flag] "i" (flags), \
+ [size] "i" (sizeof(struct bug_entry)), ##__VA_ARGS__); \
} while (0)
#endif /* CONFIG_DEBUG_BUGVERBOSE */
--- a/arch/x86/include/asm/kasan.h
+++ b/arch/x86/include/asm/kasan.h
@@ -2,7 +2,10 @@
#ifndef _ASM_X86_KASAN_H
#define _ASM_X86_KASAN_H
+#include <asm/bug.h>
+
#include <linux/const.h>
+#include <linux/sched.h>
#define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
#define KASAN_SHADOW_SCALE_SHIFT 3
@@ -26,8 +29,22 @@
#ifndef __ASSEMBLY__
#ifdef CONFIG_KASAN
+
void __init kasan_early_init(void);
void __init kasan_init(void);
+
+static __always_inline void
+kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
+{
+ if (!current->kasan_depth) {
+ unsigned long rdi = addr, rsi = size, rdx = is_write, rcx = ip;
+ _BUG_FLAGS(ASM_UD2, BUGFLAG_KASAN,
+ "D" (rdi), "S" (rsi), "d" (rdx), "c" (rcx));
+ annotate_reachable();
+ }
+}
+#define kasan_report kasan_report
+
#else
static inline void kasan_early_init(void) { }
static inline void kasan_init(void) { }
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -10,6 +10,7 @@
#define BUGFLAG_WARNING (1 << 0)
#define BUGFLAG_ONCE (1 << 1)
#define BUGFLAG_DONE (1 << 2)
+#define BUGFLAG_KASAN (1 << 3)
#define BUGFLAG_TAINT(taint) ((taint) << 8)
#define BUG_GET_TAINT(bug) ((bug)->flags >> 8)
#endif
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -83,6 +83,9 @@ size_t kasan_metadata_size(struct kmem_c
bool kasan_save_enable_multi_shot(void);
void kasan_restore_multi_shot(bool enabled);
+void __kasan_report(unsigned long addr, size_t size,
+ bool is_write, unsigned long ip);
+
#else /* CONFIG_KASAN */
static inline void kasan_unpoison_shadow(const void *address, size_t size) {}
@@ -153,8 +156,14 @@ static inline void kasan_remove_zero_sha
static inline void kasan_unpoison_slab(const void *ptr) { }
static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
+static inline void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip) { }
+
#endif /* CONFIG_KASAN */
+#ifndef kasan_report
+#define kasan_report(addr, size, is_write, ip) __kasan_report(addr, size, is_write, ip)
+#endif
+
#ifdef CONFIG_KASAN_GENERIC
#define KASAN_SHADOW_INIT 0
@@ -177,9 +186,6 @@ 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);
-
#else /* CONFIG_KASAN_SW_TAGS */
static inline void kasan_init_tags(void) { }
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -47,6 +47,7 @@
#include <linux/bug.h>
#include <linux/sched.h>
#include <linux/rculist.h>
+#include <linux/kasan.h>
extern struct bug_entry __start___bug_table[], __stop___bug_table[];
@@ -144,7 +145,7 @@ enum bug_trap_type report_bug(unsigned l
{
struct bug_entry *bug;
const char *file;
- unsigned line, warning, once, done;
+ unsigned line, warning, once, done, kasan;
if (!is_valid_bugaddr(bugaddr))
return BUG_TRAP_TYPE_NONE;
@@ -167,6 +168,7 @@ enum bug_trap_type report_bug(unsigned l
line = bug->line;
#endif
warning = (bug->flags & BUGFLAG_WARNING) != 0;
+ kasan = (bug->flags & BUGFLAG_KASAN) != 0;
once = (bug->flags & BUGFLAG_ONCE) != 0;
done = (bug->flags & BUGFLAG_DONE) != 0;
@@ -188,6 +190,11 @@ enum bug_trap_type report_bug(unsigned l
return BUG_TRAP_TYPE_WARN;
}
+ if (kasan) {
+ __kasan_report(regs->di, regs->si, regs->dx, regs->cx);
+ return BUG_TRAP_TYPE_WARN;
+ }
+
printk(KERN_DEFAULT CUT_HERE);
if (file)
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -130,7 +130,7 @@ void check_memory_region(unsigned long a
void *find_first_bad_addr(void *addr, size_t size);
const char *get_bug_type(struct kasan_access_info *info);
-void kasan_report(unsigned long addr, size_t size,
+void __kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip);
void kasan_report_invalid_free(void *object, unsigned long ip);
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -281,7 +281,7 @@ void kasan_report_invalid_free(void *obj
end_report(&flags);
}
-void kasan_report(unsigned long addr, size_t size,
+void __kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip)
{
struct kasan_access_info info;