linux-kernel - [PATCH] ARM: rename missed uaccess .fixup section

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Date:   Fri, 7 Feb 2020 18:02:51 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Nicolas Pitre <nico@...xnic.net>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Manoj Gupta <manojgupta@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] ARM: rename missed uaccess .fixup section

When the uaccess .fixup section was renamed to .text.fixup, one case was
missed. Under ld.bfd, the orphaned section was moved close to .text
(since they share the "ax" bits), so things would work normally on
uaccess faults. Under ld.lld, the orphaned section was placed outside
the .text section, making it unreachable. Rename the missed section.

Link: https://github.com/ClangBuiltLinux/linux/issues/282
Link: https://bugs.chromium.org/p/chromium/issues/detail?id=1020633#c44
Link: https://lore.kernel.org/r/nycvar.YSQ.7.76.1912032147340.17114@knanqh.ubzr
Fixes: c4a84ae39b4a5 ("ARM: 8322/1: keep .text and .fixup regions closer together")
Cc: stable@...r.kernel.org
Reported-by: Nathan Chancellor <natechancellor@...il.com>
Reported-by: Manoj Gupta <manojgupta@...gle.com>
Debugged-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
I completely missed this the first several times I looked at this
problem. Thank you Nicolas for pushing back on the earlier patch!
Manoj or Nathan, can you test this?
---
 arch/arm/lib/copy_from_user.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/lib/copy_from_user.S b/arch/arm/lib/copy_from_user.S
index 95b2e1ce559c..f8016e3db65d 100644
--- a/arch/arm/lib/copy_from_user.S
+++ b/arch/arm/lib/copy_from_user.S
@@ -118,7 +118,7 @@ ENTRY(arm_copy_from_user)
 
 ENDPROC(arm_copy_from_user)
 
-	.pushsection .fixup,"ax"
+	.pushsection .text.fixup,"ax"
 	.align 0
 	copy_abort_preamble
 	ldmfd	sp!, {r1, r2, r3}
-- 
2.20.1


-- 
Kees Cook