Re: [PATCH 7/7] modpost: handle relocations mismatch in __ex_table.

[Thierry Reding <thierry.reding@gmail.com>]

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On Tue, Mar 17, 2015 at 01:40:02PM +0100, Quentin Casasnovas wrote:
> __ex_table is a simple table section where each entry is a pair of
> addresses - the first address is an address which can fault in kernel
> space, and the second address points to where the kernel should jump to
> when handling that fault.  This is how copy_from_user() does not crash the
> kernel if userspace gives a borked pointer for example.
> 
> If one of these addresses point to a non-executable section, something is
> seriously wrong since it either means the kernel will never fault from
> there or it will not be able to jump to there.  As both cases are serious
> enough, we simply error out in these cases so the build fails and the
> developper has to fix the issue.
> 
> In case the section is executable, but it isn't referenced in our list of
> authorized sections to point to from __ex_table, we just dump a warning
> giving more information about it.  We do this in case the new section is
> executable but isn't supposed to be executed by the kernel.  This happened
> with .altinstr_replacement, which is executable but is only used to copy
> instructions from - we should never have our instruction pointer pointing
> in .altinstr_replacement.  Admitedly, a proper fix in that case would be to
> just set .altinstr_replacement NX, but we need to warn about future cases
> like this.
> 
> Signed-off-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
> ---
>  scripts/mod/modpost.c | 141 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 141 insertions(+)

This causes a bunch of mismatch warnings on 32-bit and 64-bit ARM
because there are two additional sections, .text.fixup and
.exception.text that store executable code. I've attached a patch
to fix those, but feel free to squash that into the original commit
if that's still possible.

Also adding Rusty since he applied this to the modules-next tree.

Thierry

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From f5199120caafa0056cb18808ffe15af41bb102f3 Mon Sep 17 00:00:00 2001
From: Thierry Reding <treding@nvidia.com>
Date: Tue, 14 Apr 2015 13:59:07 +0200
Subject: [PATCH] modpost: Whitelist .text.fixup and .exception.text

32-bit and 64-bit ARM use these sections to store executable code, so
they must be whitelisted in modpost's table of valid text sections.

Signed-off-by: Thierry Reding <treding@nvidia.com>
---
 scripts/mod/modpost.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index cbd53e08769d..6a925f200b25 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -876,7 +876,7 @@ static void check_section(const char *modname, struct elf_info *elf,
 #define TEXT_SECTIONS ".text", ".text.unlikely", ".sched.text", \
 		".kprobes.text"
 #define OTHER_TEXT_SECTIONS ".ref.text", ".head.text", ".spinlock.text", \
-		".fixup", ".entry.text"
+		".fixup", ".entry.text", ".text.fixup", ".exception.text"
 
 #define INIT_SECTIONS      ".init.*"
 #define MEM_INIT_SECTIONS  ".meminit.*"
-- 
2.3.5


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