Re: strace-4.18 test suite oopses sparc64 4.12 and 4.13-rc kernels
From: David Miller
Date: Wed Aug 02 2017 - 19:27:42 EST
From: Sam Ravnborg <sam@xxxxxxxxxxxx>
Date: Wed, 2 Aug 2017 23:36:47 +0200
> And memset calls down to bzero, where %o0=buf, %o1=len
> %o0 = 0xc
> %o1 = 0xfff000123c897a80
> %o2 = 0x0
> %o3 = 0xc
> So from this we know that:
> res = 0xfff000123c897a80
> to + (n - 0xfff000123c897a80)) = 0xc
> The value "fff000123c897a80" really looks like a constructed address
> from somewhere in the strace code, and where this constructed address
> is used to provoke some unusual behaviour.
> The "fff0" part may be a sparc thing.
> So far the analysis seems to match the intial conclusion that
> we in this special case try to zero out the remaining memory
> based on the return value of raw_copy_from_user.
> And therefore we use the return value (res) which triggers the oops.
Yes, the return value is bogus.
> So rather than manipulating with the assembler code as suggested
> in the previous mail this simpler patch could be tested:
> - memset(to + (n - res), 0, res);
> + void: /*memset(to + (n - res), 0, res);*/
Need a semicolon rather than a colon there :-)