linux-kernel - [PATCH 4.4 13/20] [PATCH] x86: livepatch: Treat R_X86_64_PLT32 as R_X86_64

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Message-Id: <20190221141947.151506933@linuxfoundation.org>
Date:   Thu, 21 Feb 2019 15:35:43 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, chenzefeng <chenzefeng2@...wei.com>,
        Petr Mladek <pmladek@...e.com>
Subject: [PATCH 4.4 13/20] [PATCH] x86: livepatch: Treat R_X86_64_PLT32 as R_X86_64_PC32

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

Signed-off-by: chenzefeng <chenzefeng2@...wei.com>

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>
Reviewed-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kernel/livepatch.c |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/x86/kernel/livepatch.c
+++ b/arch/x86/kernel/livepatch.c
@@ -58,6 +58,7 @@ int klp_write_module_reloc(struct module
 		val = (s32)value;
 		break;
 	case R_X86_64_PC32:
+	case R_X86_64_PLT32:
 		val = (u32)(value - loc);
 		break;
 	default: