Messages in this thread | | | From | Andrey Konovalov <> | Date | Wed, 13 Nov 2019 16:19:01 +0100 | Subject | Re: [PATCH 3/3] x86/kasan: Print original address on #GP |
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On Wed, Nov 13, 2019 at 11:11 AM 'Dmitry Vyukov' via kasan-dev <kasan-dev@googlegroups.com> wrote: > > On Tue, Nov 12, 2019 at 10:10 PM 'Jann Horn' via kasan-dev > <kasan-dev@googlegroups.com> wrote: > > > > Make #GP exceptions caused by out-of-bounds KASAN shadow accesses easier > > to understand by computing the address of the original access and > > printing that. More details are in the comments in the patch. > > > > This turns an error like this: > > > > kasan: CONFIG_KASAN_INLINE enabled > > kasan: GPF could be caused by NULL-ptr deref or user memory access > > traps: dereferencing non-canonical address 0xe017577ddf75b7dd > > general protection fault: 0000 [#1] PREEMPT SMP KASAN PTI > > > > into this: > > > > traps: dereferencing non-canonical address 0xe017577ddf75b7dd > > kasan: maybe dereferencing invalid pointer in range > > [0x00badbeefbadbee8-0x00badbeefbadbeef] > > general protection fault: 0000 [#3] PREEMPT SMP KASAN PTI > > [...]
Would it make sense to use the common "BUG: KASAN: <bug-type>" report format here? Something like:
BUG: KASAN: invalid-ptr-deref in range ...
Otherwise this looks amazing, distinguishing NULL pointer accesses from wild memory accesses is much more convenient with this. Thanks Jann!
> > Nice! > > +Andrey, do you see any issues for TAGS mode? Or, Jann, did you test > it by any chance?
Hm, this looks like x86-specific change, so I don't think it interferes with the TAGS mode.
> > > > Signed-off-by: Jann Horn <jannh@google.com> > > --- > > arch/x86/include/asm/kasan.h | 6 +++++ > > arch/x86/kernel/traps.c | 2 ++ > > arch/x86/mm/kasan_init_64.c | 52 +++++++++++++++++++++++++----------- > > 3 files changed, 44 insertions(+), 16 deletions(-) > > > > diff --git a/arch/x86/include/asm/kasan.h b/arch/x86/include/asm/kasan.h > > index 13e70da38bed..eaf624a758ed 100644 > > --- a/arch/x86/include/asm/kasan.h > > +++ b/arch/x86/include/asm/kasan.h > > @@ -25,6 +25,12 @@ > > > > #ifndef __ASSEMBLY__ > > > > +#ifdef CONFIG_KASAN_INLINE > > +void kasan_general_protection_hook(unsigned long addr); > > +#else > > +static inline void kasan_general_protection_hook(unsigned long addr) { } > > +#endif > > + > > #ifdef CONFIG_KASAN > > void __init kasan_early_init(void); > > void __init kasan_init(void); > > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > > index 479cfc6e9507..e271a5a1ddd4 100644 > > --- a/arch/x86/kernel/traps.c > > +++ b/arch/x86/kernel/traps.c > > @@ -58,6 +58,7 @@ > > #include <asm/umip.h> > > #include <asm/insn.h> > > #include <asm/insn-eval.h> > > +#include <asm/kasan.h> > > > > #ifdef CONFIG_X86_64 > > #include <asm/x86_init.h> > > @@ -544,6 +545,7 @@ static void print_kernel_gp_address(struct pt_regs *regs) > > return; > > > > pr_alert("dereferencing non-canonical address 0x%016lx\n", addr_ref); > > + kasan_general_protection_hook(addr_ref); > > #endif > > } > > > > diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c > > index 296da58f3013..9ef099309489 100644 > > --- a/arch/x86/mm/kasan_init_64.c > > +++ b/arch/x86/mm/kasan_init_64.c > > @@ -246,20 +246,44 @@ static void __init kasan_map_early_shadow(pgd_t *pgd) > > } > > > > #ifdef CONFIG_KASAN_INLINE > > -static int kasan_die_handler(struct notifier_block *self, > > - unsigned long val, > > - void *data) > > +/* > > + * With CONFIG_KASAN_INLINE, accesses to bogus pointers (outside the high > > + * canonical half of the address space) cause out-of-bounds shadow memory reads > > + * before the actual access. For addresses in the low canonical half of the > > + * address space, as well as most non-canonical addresses, that out-of-bounds > > + * shadow memory access lands in the non-canonical part of the address space, > > + * causing #GP to be thrown. > > + * Help the user figure out what the original bogus pointer was. > > + */ > > +void kasan_general_protection_hook(unsigned long addr) > > { > > - if (val == DIE_GPF) { > > - pr_emerg("CONFIG_KASAN_INLINE enabled\n"); > > - pr_emerg("GPF could be caused by NULL-ptr deref or user memory access\n"); > > - } > > - return NOTIFY_OK; > > -} > > + unsigned long orig_addr; > > + const char *addr_type; > > + > > + if (addr < KASAN_SHADOW_OFFSET) > > + return; > > Thinking how much sense it makes to compare addr with KASAN_SHADOW_END... > If the addr is > KASAN_SHADOW_END, we know it's not a KASAN access, > but do we ever get GP on canonical addresses? > > > > > -static struct notifier_block kasan_die_notifier = { > > - .notifier_call = kasan_die_handler, > > -}; > > + orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT; > > + /* > > + * For faults near the shadow address for NULL, we can be fairly certain > > + * that this is a KASAN shadow memory access. > > + * For faults that correspond to shadow for low canonical addresses, we > > + * can still be pretty sure - that shadow region is a fairly narrow > > + * chunk of the non-canonical address space. > > + * But faults that look like shadow for non-canonical addresses are a > > + * really large chunk of the address space. In that case, we still > > + * print the decoded address, but make it clear that this is not > > + * necessarily what's actually going on. > > + */ > > + if (orig_addr < PAGE_SIZE) > > + addr_type = "dereferencing kernel NULL pointer"; > > + else if (orig_addr < TASK_SIZE_MAX) > > + addr_type = "probably dereferencing invalid pointer"; > > This is access to user memory, right? In outline mode we call it > "user-memory-access". We could say about "user" part here as well.
I think we should use the same naming scheme here as in get_wild_bug_type(): null-ptr-deref, user-memory-access and wild-memory-access.
> > > + else > > + addr_type = "maybe dereferencing invalid pointer"; > > + pr_alert("%s in range [0x%016lx-0x%016lx]\n", addr_type, > > + orig_addr, orig_addr + (1 << KASAN_SHADOW_SCALE_SHIFT) - 1); > > "(1 << KASAN_SHADOW_SCALE_SHIFT) - 1)" part may be replaced with > KASAN_SHADOW_MASK. > Overall it can make sense to move this mm/kasan/report.c b/c we are > open-coding a number of things here (e.g. reverse address mapping). If > another arch will do the same, it will need all of this code too (?). > > But in general I think it's a very good usability improvement for KASAN. > > > +} > > #endif > > > > void __init kasan_early_init(void) > > @@ -298,10 +322,6 @@ void __init kasan_init(void) > > int i; > > void *shadow_cpu_entry_begin, *shadow_cpu_entry_end; > > > > -#ifdef CONFIG_KASAN_INLINE > > - register_die_notifier(&kasan_die_notifier); > > -#endif > > - > > memcpy(early_top_pgt, init_top_pgt, sizeof(early_top_pgt)); > > > > /* > > -- > > 2.24.0.432.g9d3f5f5b63-goog > > > > -- > > You received this message because you are subscribed to the Google Groups "kasan-dev" group. > > To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@googlegroups.com. > > To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/20191112211002.128278-3-jannh%40google.com. > > -- > You received this message because you are subscribed to the Google Groups "kasan-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/CACT4Y%2BaojSsss3%2BY2FB9Rw%3DOPxXgsFrGF0YiAJ9eo2wJM0ruWg%40mail.gmail.com.
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