From: Konrad Rzeszutek Wilk <konrad@kernel.org>
To: Jan Beulich <jbeulich@suse.com>
Cc: andrew.cooper3@citrix.com, julien.grall@arm.com,
sstabellini@kernel.org, xen-devel@lists.xenproject.org
Subject: Re: [PATCH v2 3/5] xen/livepatch/ARM32: Don't load and crash on livepatches loaded with wrong alignment.
Date: Thu, 7 Sep 2017 13:36:46 -0400 [thread overview]
Message-ID: <20170907173644.GA7717@localhost.localdomain> (raw)
In-Reply-To: <59819945020000780010323D@prv-mh.provo.novell.com>
On Wed, Aug 02, 2017 at 03:20:05AM -0600, Jan Beulich wrote:
> >>> Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> 07/31/17 6:04 PM >>>
> >On Mon, Jul 31, 2017 at 07:55:34AM -0600, Jan Beulich wrote:
> >> >>> Konrad Rzeszutek Wilk <konrad@kernel.org> 07/26/17 9:50 PM >>>
> >> >--- a/docs/misc/livepatch.markdown
> >> >+++ b/docs/misc/livepatch.markdown
> >> >@@ -279,6 +279,10 @@ It may also have some architecture-specific sections. For example:
> >> >* Exception tables.
> >> >* Relocations for each of these sections.
> >> >
> >> >+Note that on ARM 32 the sections SHOULD be four byte aligned. Otherwise
> >> >+we risk hitting Data Abort exception as un-aligned manipulation of data is
> >> >+prohibited on ARM 32.
> >>
> >> This (and hence the rest of the patch) is not in line with the outcome of the
> >> earlier discussion we had. Nothing is wrong with a section having smaller
> >> alignment, as long as there are no 32-bit (or wider, but I don't think there
> >> are any such) relocations against such a section. And even if there were, I
> >> think it should rather be the code doing the relocations needing to cope, as
> >> I don't think the ARM ELF ABI imposes any such restriction.
> >
> >The idea behind this patch is to give advance warnings. Akin to what
> >2ff229643b739e2fd0cd0536ee9fca506cfa92f8
> >"xen/livepatch: Don't crash on encountering STN_UNDEF relocations" did.
> >
> >The other patches in this series fix the alignment issues.
> >
> >The ARM ELF ABI (http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044f/IHI0044F_aaelf.pdf)
> >
> >says:
> >
> >4.3.5 Section Alignment
> >There is no minimum alignment required for a section. However, sections containing thumb code must be at least
> >16-bit aligned and sections containing ARM code must be at least 32-bit aligned.
> >Platform standards may set a limit on the maximum alignment that they can guarantee (normally the page size).
>
> Note the "thumb code" and "ARM code" in here - iirc you're checking _all_
> sections, not just ones containing code.
I can fix the code to only do the check for 'X' ones:
[ 2] .text PROGBITS 0000000000000000 00000070
00000000000000ca 0000000000000000 AX 0 0 16
[ 4] .altinstr_replace PROGBITS 0000000000000000 0000013c
000000000000000b 0000000000000000 AX 0 0 4
[ 5] .fixup PROGBITS 0000000000000000 00000147
000000000000000d 0000000000000000 AX 0 0 1
And also have the check in the relocation - which right now are
32-bit: R_ARM_ABS32, R_ARM_REL32, R_ARM_MOVW_ABS_NC, R_ARM_MOVT_ABS,
R_ARM_CALL, R_ARM_JUMP24 so will leave the code as in
arch_livepatch_perform.
But neither one of those is going to help in catching livepatches
that have the wrong alignment without relocations and not executable.
For example .livepatch.depends
Thoughts on how you would want to catch those?
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next prev parent reply other threads:[~2017-09-07 17:36 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-26 19:47 [PATCH v2] Livepatch fixes for v4.10 (v2) Konrad Rzeszutek Wilk
2017-07-26 19:47 ` [PATCH v2 1/5] livepatch: Tighten alignment checks Konrad Rzeszutek Wilk
2017-07-31 13:46 ` Jan Beulich
2017-07-26 19:47 ` [PATCH v2 2/5] livepatch: Include sizes when an mismatch occurs Konrad Rzeszutek Wilk
2017-07-31 13:51 ` Jan Beulich
2017-07-26 19:47 ` [PATCH v2 3/5] xen/livepatch/ARM32: Don't load and crash on livepatches loaded with wrong alignment Konrad Rzeszutek Wilk
2017-07-26 22:27 ` Andrew Cooper
2017-07-31 13:55 ` Jan Beulich
2017-07-31 16:04 ` Konrad Rzeszutek Wilk
2017-08-02 9:20 ` Jan Beulich
2017-09-07 17:36 ` Konrad Rzeszutek Wilk [this message]
2017-09-08 9:30 ` Jan Beulich
2017-09-09 12:05 ` Konrad Rzeszutek Wilk
2017-09-11 9:01 ` Jan Beulich
2017-09-12 0:22 ` Konrad Rzeszutek Wilk
2017-09-12 8:57 ` Jan Beulich
2017-09-18 19:37 ` Konrad Rzeszutek Wilk
2017-09-19 15:04 ` Jan Beulich
2017-09-20 15:12 ` Konrad Rzeszutek Wilk
2017-09-20 15:51 ` Jan Beulich
2017-07-26 19:47 ` [PATCH v2 4/5] alternative/x86/arm32: Align altinstructions (and altinstr_replacement) sections Konrad Rzeszutek Wilk
2017-07-31 14:01 ` Jan Beulich
2017-09-11 18:59 ` Konrad Rzeszutek Wilk
2017-07-26 19:47 ` [PATCH v2 5/5] livepatch: Declare live patching as a supported feature Konrad Rzeszutek Wilk
2017-07-31 14:03 ` Jan Beulich
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