linux-kernel - [PATCH v2] x86: vdso: Pass --eh-frame-hdr to ld

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Message-Id: <20181214223637.35954-1-astrachan@google.com>
Date:   Fri, 14 Dec 2018 14:36:37 -0800
From:   Alistair Strachan <astrachan@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     Florian Weimer <fweimer@...hat.com>,
        "Carlos O'Donell" <carlos@...hat.com>,
        "H. J. Lu" <hjl.tools@...il.com>,
        Laura Abbott <labbott@...hat.com>, stable@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        kernel-team@...roid.com
Subject: [PATCH v2] x86: vdso: Pass --eh-frame-hdr to ld

Commit 379d98ddf413 ("x86: vdso: Use $LD instead of $CC to link")
accidentally broke unwinding from userspace, because ld would strip the
.eh_frame sections when linking.

Originally, the compiler would implicitly add --eh-frame-hdr when
invoking the linker, but when this Makefile was converted from invoking
ld via the compiler, to invoking it directly (like vmlinux does),
the flag was missed. (The EH_FRAME section is important for the VDSO
shared libraries, but not for vmlinux.)

Fix the problem by explicitly specifying --eh-frame-hdr, which restores
parity with the old method.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201741
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1659295
Reported-by: Florian Weimer <fweimer@...hat.com>
Reported-by: Carlos O'Donell <carlos@...hat.com>
Reported-by: "H. J. Lu" <hjl.tools@...il.com>
Tested-by: Laura Abbott <labbott@...hat.com>
Fixes: 379d98ddf413 ("x86: vdso: Use $LD instead of $CC to link")
Cc: stable@...r.kernel.org
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: X86 ML <x86@...nel.org>
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: kernel-team@...roid.com
Signed-off-by: Alistair Strachan <astrachan@...gle.com>
---
v2: Updated commit message, no changes to the code
 arch/x86/entry/vdso/Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 141d415a8c80..c3d7ccd25381 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -171,7 +171,8 @@ quiet_cmd_vdso = VDSO    $@
 		 sh $(srctree)/$(src)/checkundef.sh '$(NM)' '$@'
 
 VDSO_LDFLAGS = -shared $(call ld-option, --hash-style=both) \
-	$(call ld-option, --build-id) -Bsymbolic
+	$(call ld-option, --build-id) $(call ld-option, --eh-frame-hdr) \
+	-Bsymbolic
 GCOV_PROFILE := n
 
 #
-- 
2.20.0.405.gbc1bbc6f85-goog