Re: [PATCH 5/6] objtool: Add UACCESS validation

Peter Zijlstra
2019-02-27T17:28:32Z

On Wed, Feb 27, 2019 at 04:40:28PM +0100, Dmitry Vyukov wrote:
> On Wed, Feb 27, 2019 at 3:33 PM Peter Zijlstra <peterz@infradead.org> wrote:

> > Urgh, kasan_report() is definitely unsafe. Now, admitedly we should
> > 'never' hit that, but it does leave us up a creek without a paddle.

> If SMAP detects additional bugs, then it would be pity to disable it
> with KASAN (detect bugs in production but not during testing).
>
> You mentioned that exception save/restore the UACCESS state. Is it
> possible to do the same in kasan_report? At the very least we need to
> survive report printing, what happens after that does not matter much
> (we've corrupted memory by now anyway).

Ideally we'll put all of kasan_report() in an exception, much like we do
for WARN. But there's a distinct lack of arch hooks there to play with.
I suppose I can try and create some.

On top of that we'll have to mark these __asan functions with notrace.

Maybe a little something horrible like so... completely untested.

---
arch/x86/include/asm/bug.h | 28 ++++++++++++++--------------
arch/x86/include/asm/kasan.h | 11 +++++++++++
include/asm-generic/bug.h | 1 +
include/linux/kasan.h | 6 +++++-
lib/bug.c | 8 +++++++-
mm/kasan/generic.c | 4 ++--
mm/kasan/kasan.h | 2 +-
mm/kasan/report.c | 2 +-
8 files changed, 42 insertions(+), 20 deletions(-)

diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index 6804d6642767..ead3e6ad4eb6 100644
--- 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[flags]" "\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__), \
+ [flags] "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[flags]" "\t# bug_entry::flags\n" \
+ "\t.org 2b+%c[size]\n" \
".popsection" \
- : : "i" (flags), \
- "i" (sizeof(struct bug_entry))); \
+ : : [flags] "i" (flags), \
+ [size] "i" (sizeof(struct bug_entry)), ##__VA_ARGS__); \
} while (0)

#endif /* CONFIG_DEBUG_BUGVERBOSE */
diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h
index 13e70da38bed..b7d563965b4d 100644
--- a/arch/x86/include/asm/kasan.h
+++ b/arch/x86/include/asm/kasan.h
@@ -2,6 +2,8 @@
#ifndef _ASM_X86_KASAN_H
#define _ASM_X86_KASAN_H

+#include <asm/bug.h>
+
#include <linux/const.h>
#define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
#define KASAN_SHADOW_SCALE_SHIFT 3
@@ -26,8 +28,17 @@
#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)
+{
+ unsigned long rdi = addr, rsi = size, rdx = is_write, rdx = ip;
+
+ _BUG_FLAGS(ASM_UD2, BUGFLAG_KASAN, "D" (rdi), "S" (rsi), "d" (rdx), "c" (rcx));
+}
+
#else
static inline void kasan_early_init(void) { }
static inline void kasan_init(void) { }
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 0e9bd9c83870..6c829e80ea2a 100644
--- 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
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index b40ea104dd36..0ab50faedc9e 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -177,7 +177,7 @@ void kasan_init_tags(void);

void *kasan_reset_tag(const void *addr);

-void kasan_report(unsigned long addr, size_t size,
+void __kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip);

#else /* CONFIG_KASAN_SW_TAGS */
@@ -191,4 +191,8 @@ static inline void *kasan_reset_tag(const void *addr)

#endif /* CONFIG_KASAN_SW_TAGS */

+#ifndef kasan_report
+#define kasan_report(addr, size, is_write, ip) __kasan_report(addr, size, is_write, ip)
+#endif
+
#endif /* LINUX_KASAN_H */
diff --git a/lib/bug.c b/lib/bug.c
index 1077366f496b..c9c005a35b76 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -144,7 +144,7 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
{
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 +167,7 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
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 +189,11 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
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)
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index ccb6207276e3..84be578e2591 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -228,7 +228,7 @@ void __asan_unregister_globals(struct kasan_global *globals, size_t size)
EXPORT_SYMBOL(__asan_unregister_globals);

#define DEFINE_ASAN_LOAD_STORE(size) \
- void __asan_load##size(unsigned long addr) \
+ notrace void __asan_load##size(unsigned long addr) \
{ \
check_memory_region_inline(addr, size, false, _RET_IP_);\
} \
@@ -236,7 +236,7 @@ EXPORT_SYMBOL(__asan_unregister_globals);
__alias(__asan_load##size) \
void __asan_load##size##_noabort(unsigned long); \
EXPORT_SYMBOL(__asan_load##size##_noabort); \
- void __asan_store##size(unsigned long addr) \
+ notrace void __asan_store##size(unsigned long addr) \
{ \
check_memory_region_inline(addr, size, true, _RET_IP_); \
} \
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index ea51b2d898ec..7bc954b4fc2d 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -130,7 +130,7 @@ void check_memory_region(unsigned long addr, size_t size, bool write,
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);

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index ca9418fe9232..1d5050659388 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -281,7 +281,7 @@ void kasan_report_invalid_free(void *object, unsigned long ip)
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;