Messages in this thread | | | Subject | Re: [PATCH] x86/mpx: fix recursive munmap() corruption | From | Christophe Leroy <> | Date | Fri, 23 Oct 2020 14:28:52 +0200 |
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Hi Laurent
Le 07/05/2019 à 18:35, Laurent Dufour a écrit : > Le 01/05/2019 à 12:32, Michael Ellerman a écrit : >> Laurent Dufour <ldufour@linux.vnet.ibm.com> writes: >>> Le 23/04/2019 à 18:04, Dave Hansen a écrit : >>>> On 4/23/19 4:16 AM, Laurent Dufour wrote: >> ... >>>>> There are 2 assumptions here: >>>>> 1. 'start' and 'end' are page aligned (this is guaranteed by __do_munmap(). >>>>> 2. the VDSO is 1 page (this is guaranteed by the union vdso_data_store on powerpc) >>>> >>>> Are you sure about #2? The 'vdso64_pages' variable seems rather >>>> unnecessary if the VDSO is only 1 page. ;) >>> >>> Hum, not so sure now ;) >>> I got confused, only the header is one page. >>> The test is working as a best effort, and don't cover the case where >>> only few pages inside the VDSO are unmmapped (start > >>> mm->context.vdso_base). This is not what CRIU is doing and so this was >>> enough for CRIU support. >>> >>> Michael, do you think there is a need to manage all the possibility >>> here, since the only user is CRIU and unmapping the VDSO is not a so >>> good idea for other processes ? >> >> Couldn't we implement the semantic that if any part of the VDSO is >> unmapped then vdso_base is set to zero? That should be fairly easy, eg: >> >> if (start < vdso_end && end >= mm->context.vdso_base) >> mm->context.vdso_base = 0; >> >> >> We might need to add vdso_end to the mm->context, but that should be OK. >> >> That seems like it would work for CRIU and make sense in general? > > Sorry for the late answer, yes this would make more sense. > > Here is a patch doing that. >
In your patch, the test seems overkill:
+ if ((start <= vdso_base && vdso_end <= end) || /* 1 */ + (vdso_base <= start && start < vdso_end) || /* 3,4 */ + (vdso_base < end && end <= vdso_end)) /* 2,3 */ + mm->context.vdso_base = mm->context.vdso_end = 0;
What about
if (start < vdso_end && vdso_start < end) mm->context.vdso_base = mm->context.vdso_end = 0;
This should cover all cases, or am I missing something ?
And do we really need to store vdso_end in the context ? I think it should be possible to re-calculate it: the size of the VDSO should be (&vdso32_end - &vdso32_start) + PAGE_SIZE for 32 bits VDSO, and (&vdso64_end - &vdso64_start) + PAGE_SIZE for the 64 bits VDSO.
Christophe
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