Messages in this thread | | | Date | Tue, 26 Jul 2022 08:35:43 -0700 | From | Yury Norov <> | Subject | Re: Linux 5.19-rc8 |
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On Tue, Jul 26, 2022 at 10:12:21AM +0100, Russell King (Oracle) wrote: > On Mon, Jul 25, 2022 at 10:55:18AM -0700, Linus Torvalds wrote: > > On Mon, Jul 25, 2022 at 9:11 AM Guenter Roeck <linux@roeck-us.net> wrote: > > > > > > BUG: KFENCE: out-of-bounds read in _find_next_bit_le+0x10/0x48 > > > > Ok, I was hoping somebody more ARMy would look at this, particularly > > since there is no call trace beyond the actual fault. > > First I'm aware of it. Was it reported to linux-arm-kernel? I'm guessing > the report wasn't Cc'd to me - I can't find anything in my mailbox about > it. > > > I think the fix might be something like this: > > > > diff --git a/arch/arm/lib/findbit.S b/arch/arm/lib/findbit.S > > index b5e8b9ae4c7d..b36ca301892e 100644 > > --- a/arch/arm/lib/findbit.S > > +++ b/arch/arm/lib/findbit.S > > @@ -83,6 +83,8 @@ ENDPROC(_find_first_bit_le) > > ENTRY(_find_next_bit_le) > > teq r1, #0 > > beq 3b > > + cmp r2, r1 > > + bhs 3b > > ands ip, r2, #7 > > beq 1b @ If new byte, goto old routine > > ARM( ldrb r3, [r0, r2, lsr #3] ) > > > > but my ARM asm is so broken that the above is just really random noise > > that may or may not build - much less work. > > > > I'll leave it to Russell &co to have a tested and working patch. > > I think it needs a bit more than that, but as you point out in later > emails, the compiler may do a better job for this. > > One of the reasons for using byte loads was to avoid problems in the > early days of Linux where these took void pointers and thus could be > misaligned - and using word accesses would have resulted in much > pain. However, that was changed to unsigned long pointers back in > 2017, so in theory that should no longer be a concern. > > I don't remember why we used void pointers there originally - that's > something which dates back to the 1990s.
OK, then I'm sending the patch that switches it to generic code.
Thanks, Yury
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