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    SubjectRe: [PATCH 1/8] kasan,x86: Frob kasan_report() in an exception
    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@infradead.org> 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@infradead.org>
    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@infradead.org>
    ---
    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;
    \
     
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      Last update: 2019-03-01 15:47    [W:4.536 / U:0.144 seconds]
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