Messages in this thread | | | Date | Wed, 20 Nov 2019 12:40:31 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH v2 2/3] x86/traps: Print non-canonical address on #GP |
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* Borislav Petkov <bp@alien8.de> wrote:
> On Mon, Nov 18, 2019 at 05:29:42PM +0100, Dmitry Vyukov wrote: > > > And of not having a standard way to signal "this line starts something > > > that should be reported as a bug"? Maybe as a longer-term idea, it'd > > > help to have some sort of extra prefix byte that the kernel can print > > > to say "here comes a bug report, first line should be the subject", or > > > something like that, similar to how we have loglevels... > > > > This would be great. > > Also a way to denote crash end. > > However we have lots of special logic for subjects, not sure if kernel > > could provide good subject: > > https://github.com/google/syzkaller/blob/1daed50ac33511e1a107228a9c3b80e5c4aebb5c/pkg/report/linux.go#L537-L1588 > > Probably it could, but it won't be completely trivial. E.g. if there > > is a stall inside of a timer function, it should give the name of the > > actual timer callback as identity ("stall in timer_subsystem_foo"). Or > > for syscalls we use more disambiguation b/c "in sys_ioclt" is not much > > different than saying "there is a bug in kernel" :) > > While external tools are fine and cool, they can't really block kernel > development and printk strings format is not an ABI. And yeah, we have > this discussion each time someone proposes changes to those "magic" > strings but I guess it is about time to fix this in a way that any > future changes don't break tools. > > And so I like the idea of marking *only* the first splat with some small > prefix char as that first splat is the special and very important one. > I.e., the one where die_counter is 0. > > So I could very well imagine something like: > > ... > [ 2.523708] Write protecting the kernel read-only data: 16384k > [ 2.524729] Freeing unused kernel image (text/rodata gap) memory: 2040K > [ 2.525594] Freeing unused kernel image (rodata/data gap) memory: 368K > [ 2.541414] x86/mm: Checked W+X mappings: passed, no W+X pages found. > > <--- important first splat starts here: > > [ 2.542218] [*] general protection fault while derefing a non-canonical address 0xdfff000000000001: 0000 [#1] PREEMPT SMP > [ 2.543343] [*] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.4.0-rc8+ #8 > [ 2.544138] [*] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.1-1 04/01/2014 > [ 2.545120] [*] RIP: 0010:kernel_init+0x58/0x107 > [ 2.546055] [*] Code: 48 c7 c7 e0 5c e7 81 e8 eb d2 90 ff c7 05 77 d6 95 00 02 00 00 00 e8 4e 1d a2 ff e8 69 b7 91 ff 48 b8 01 00 00 00 00 00 ff df <ff> e0 48 8b 3d fe 54 d7 00 48 85 ff 74 22 e8 76 93 84 ff 85 c0 89
> <--- and ends here. > > to denote that first splat. And the '*' thing is just an example - it > can be any char - whatever's easier to grep for.
Well, this would break various pieces of tooling I'm sure.
Maybe it would be nicer to tooling to embedd the splat-counter in the timestamp in a way:
> [ 2.542218-#1] general protection fault while derefing a non-canonical address 0xdfff000000000001: 0000 [#1] PREEMPT SMP > [ 2.543343-#1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.4.0-rc8+ #8 > [ 2.544138-#1] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.1-1 04/01/2014 > [ 2.545120-#1] RIP: 0010:kernel_init+0x58/0x107 > [ 2.546055-#1] Code: 48 c7 c7 e0 5c e7 81 e8 eb d2 90 ff c7 05 77 d6 95 00 02 00 00 00 e8 4e 1d a2 ff e8 69 b7 91 ff 48 b8 01 00 00 00 00 00 ff df <ff> e0 48 8b 3d fe 54 d7 00 48 85 ff 74 22 e8 76 93 84 ff 85 c0 89
That way we'd not only know that it's the first splat, but we'd know it from all the *other* splats as well where they are in the splat-rank ;-)
(Also Cc:-ed Linus.)
Thanks,
Ingo
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