linux-kernel - Re: [PATCH] x86: livepatch: Treat R_X86_64_PLT32 as R_X86_64

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Message-ID: <79A62BFA453EFB42B7A4E40AD8F3A2264F2AA52F@DGGEMA503-MBX.china.huawei.com>
Date:   Tue, 19 Feb 2019 08:16:36 +0000
From:   "chenzefeng (A)" <chenzefeng2@...wei.com>
To:     Petr Mladek <pmladek@...e.com>,
        "chengjian (D)" <cj.chengjian@...wei.com>
CC:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Jiri Kosina <jikos@...nel.org>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "sjenning@...hat.com" <sjenning@...hat.com>,
        "vojtech@...e.com" <vojtech@...e.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Xiexiuqi <xiexiuqi@...wei.com>
Subject: Re: [PATCH] x86: livepatch: Treat R_X86_64_PLT32 as R_X86_64_PC32

Hi,

I am sorry this email was sent by accident. Please ignore this email.

Best Regards



-----邮件原件-----
发件人: chenzefeng (A) 
发送时间: 2019年2月19日 14:38
收件人: 'Petr Mladek' <pmladek@...e.com>; chengjian (D) <cj.chengjian@...wei.com>
抄送: 'stable@...r.kernel.org' <stable@...r.kernel.org>; Jiri Kosina <jikos@...nel.org>; hjl.tools@...il.com; jpoimboe@...hat.com; sjenning@...hat.com; vojtech@...e.com; tglx@...utronix.de; mingo@...hat.com; hpa@...or.com; gregkh@...uxfoundation.org; x86@...nel.org; live-patching@...r.kernel.org; linux-kernel@...r.kernel.org; Xiexiuqi <xiexiuqi@...wei.com>
主题: Re:[PATCH] x86: livepatch: Treat R_X86_64_PLT32 as R_X86_64_PC32

On Mon 2019-02-18 17:22, Petr wrote:

> On Mon 2019-02-18 13:29:11, chengjian (D) wrote:
> > Hi，Jiri
> >
> >
> > This patch should be merged into 4.4 stable,
> >
> > which still use klp_write_module_reloc.
> >
> >
> > https://elixir.bootlin.com/linux/v4.4.174/source/arch/x86/kernel/livep
> > atch.c
> >
> >
> > ZeFeng may have sent a stable(4.4-y) patch to the wrong mail-list(mainline).
> 
> ZeFeng or Chengjian, please, send the patch once again with stable@...r.kernel.org in CC and explanation that it is needed only for 4.4 and why.
> 
> This thread is already too long and messed to be proceed by stable people effectively.
>
> Best Regards,
> Petr

On x86-64, for 32-bit PC-relacive branches, we can generate PLT32 relocation, instead of PC32 relocation. and R_X86_64_PLT32 can be treated the same as R_X86_64_PC32 since linux kernel doesn't use PLT.

commit b21ebf2fb4cd ("x86: Treat R_X86_64_PLT32 as R_X86_64_PC32") been fixed for the module loading, but not fixed for livepatch relocation, which will fail to load livepatch with the error message as follow:
relocation failed for symbol <symbol name> at <symbol address>

This issue only effacted the kernel version from 4.0 to 4.6, becauce the function klp_write_module_reloc is introduced by:
commit b700e7f03df5 ("livepatch: kernel: add support for live patching") and deleted by: commit 425595a7fc20
("livepatch: reuse module loader code to write relocations")

Signed-off-by: chenzefeng <chenzefeng2@...wei.com>
---
 arch/x86/kernel/livepatch.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c index d1d35cc..579f8f8 100644
--- a/arch/x86/kernel/livepatch.c
+++ b/arch/x86/kernel/livepatch.c
@@ -58,6 +58,7 @@ int klp_write_module_reloc(struct module *mod, unsigned long type,
 		val = (s32)value;
 		break;
 	case R_X86_64_PC32:
+	case R_X86_64_PLT32:
 		val = (u32)(value - loc);
 		break;
 	default:
--
1.8.5.6