From: Ross Lagerwall <ross.lagerwall@citrix.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: sstabellini@kernel.org, Andrew Cooper <andrew.cooper3@citrix.com>,
julien.grall@arm.com, Jan Beulich <jbeulich@suse.com>,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH v5 06/16] livepatch: ARM/x86: Check displacement of old_addr and new_addr
Date: Fri, 23 Sep 2016 15:36:27 +0100 [thread overview]
Message-ID: <c90fd56f-e432-4124-73be-94576788e377@citrix.com> (raw)
In-Reply-To: <1474479154-20991-7-git-send-email-konrad.wilk@oracle.com>
On 09/21/2016 06:32 PM, Konrad Rzeszutek Wilk wrote:
> If the distance is too big we are in trouble - as our relocation
> distance can surely be clipped, or still have a valid width - but
> cause an overflow of distance.
>
> On various architectures the maximum displacement for a unconditional
> branch/jump varies. ARM32 is +/- 32MB, ARM64 is +/- 128MB while x86
> for 32-bit relocations is +/- 2G.
>
> Note: On x86 we could use the 64-bit jmpq instruction which
> would provide much bigger displacement to do a jump, but we would
> still have issues with the new function not being able to reach
> any of the old functions (as all the relocations would assume 32-bit
> displacement). And "furthermore would require an register or
> memory location to load/store the address to." (From Jan).
>
> On ARM the conditional branch supports even a smaller displacement
> but fortunately we are not using that.
Wouldn't this be simpler as a BUILD_BUG_ON() in arch_livepatch_init()?
Something like BUILD_BUG_ON(((XEN_VIRT_END - NR_CPUS * PAGE_SIZE) -
XEN_VIRT_START) > ARCH_LIVEPATCH_RANGE)?
And BUILD_BUG_ON(((XEN_VIRT_END - NR_CPUS * PAGE_SIZE) - XEN_VIRT_START)
> ARCH_LIVEPATCH_RANGE)
And something similar for ARM...
--
Ross Lagerwall
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next prev parent reply other threads:[~2016-09-23 14:36 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-21 17:32 [PATCH v5] Livepatch for ARM 64 and 32 Konrad Rzeszutek Wilk
2016-09-21 17:32 ` [PATCH v5 01/16] arm64: s/ALTERNATIVE/HAS_ALTERNATIVE/ Konrad Rzeszutek Wilk
2016-09-22 12:21 ` Julien Grall
2016-09-21 17:32 ` [PATCH v5 02/16] arm/x86/common: Add HAS_[ALTERNATIVE|EX_TABLE] Konrad Rzeszutek Wilk
2016-09-22 12:23 ` Julien Grall
2016-09-22 15:30 ` Ross Lagerwall
2016-09-21 17:32 ` [PATCH v5 03/16] livepatch: Reject payloads with .alternative or .ex_table if support is not built-in Konrad Rzeszutek Wilk
2016-09-23 12:47 ` Ross Lagerwall
2016-09-21 17:32 ` [PATCH v5 04/16] arm: poison initmem when it is freed Konrad Rzeszutek Wilk
2016-09-22 12:28 ` Julien Grall
2016-09-21 17:32 ` [PATCH v5 05/16] livepatch: Initial ARM64 support Konrad Rzeszutek Wilk
2016-09-22 12:49 ` Julien Grall
2016-09-23 13:38 ` Ross Lagerwall
2016-09-23 15:44 ` Konrad Rzeszutek Wilk
2016-09-27 16:42 ` Julien Grall
2016-09-21 17:32 ` [PATCH v5 06/16] livepatch: ARM/x86: Check displacement of old_addr and new_addr Konrad Rzeszutek Wilk
2016-09-22 12:55 ` Julien Grall
2016-09-23 14:36 ` Ross Lagerwall [this message]
2016-09-23 15:37 ` Konrad Rzeszutek Wilk
2016-09-23 15:59 ` Konrad Rzeszutek Wilk
2016-09-28 10:21 ` Ross Lagerwall
2016-09-21 17:32 ` [PATCH v5 07/16] livepatch: ARM 32|64: Ignore mapping symbols: $[d, a, x] Konrad Rzeszutek Wilk
2016-09-22 12:56 ` Julien Grall
2016-09-23 14:44 ` Ross Lagerwall
2016-09-23 16:13 ` Konrad Rzeszutek Wilk
2016-09-21 17:32 ` [PATCH v5 08/16] livepatch/arm/x86: Check payload for for unwelcomed symbols Konrad Rzeszutek Wilk
2016-09-22 13:00 ` Julien Grall
2016-09-23 1:29 ` Konrad Rzeszutek Wilk
2016-09-27 8:49 ` Ross Lagerwall
2016-09-23 14:49 ` Ross Lagerwall
2016-09-23 16:15 ` Konrad Rzeszutek Wilk
2016-09-21 17:32 ` [PATCH v5 09/16] livepatch: Move test-cases to their own sub-directory in test Konrad Rzeszutek Wilk
2016-09-22 13:01 ` Julien Grall
2016-09-23 14:51 ` Ross Lagerwall
2016-09-21 17:32 ` [PATCH v5 10/16] livepatch: x86, ARM, alternative: Expose FEATURE_LIVEPATCH Konrad Rzeszutek Wilk
2016-09-22 13:03 ` Julien Grall
2016-09-27 9:49 ` Ross Lagerwall
2016-09-21 17:32 ` [PATCH v5 11/16] livepatch: tests: Make them compile under ARM64 Konrad Rzeszutek Wilk
2016-09-22 13:10 ` Julien Grall
2016-09-22 19:26 ` Konrad Rzeszutek Wilk
2016-09-23 1:33 ` Konrad Rzeszutek Wilk
2016-09-23 9:50 ` Julien Grall
2016-09-27 9:49 ` Ross Lagerwall
2016-09-21 17:32 ` [PATCH v5 12/16] xen/arm32: Add an helper to invalidate all instruction caches Konrad Rzeszutek Wilk
2016-09-22 13:17 ` Julien Grall
2016-09-21 17:32 ` [PATCH v5 13/16] bug/x86/arm: Align bug_frames sections Konrad Rzeszutek Wilk
2016-09-21 17:32 ` [PATCH v5 14/16] livepatch: Initial ARM32 support Konrad Rzeszutek Wilk
2016-09-27 16:39 ` Julien Grall
2016-09-27 17:50 ` Konrad Rzeszutek Wilk
2016-09-27 23:13 ` Julien Grall
2016-09-21 17:32 ` [PATCH v5 15/16] livepatch, arm[32|64]: Share arch_livepatch_revert Konrad Rzeszutek Wilk
2016-09-23 14:59 ` Ross Lagerwall
2016-09-23 16:15 ` Konrad Rzeszutek Wilk
2016-09-21 17:32 ` [PATCH v5 16/16] livepatch: arm[32, 64], x86: NOP test-case Konrad Rzeszutek Wilk
2016-09-22 13:23 ` Julien Grall
2016-09-23 1:35 ` Konrad Rzeszutek Wilk
2016-09-23 9:53 ` Julien Grall
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