[SRU][Xenial][PATCH 1/1] x86/vdso: Pass --eh-frame-hdr to the linker

[Kleber Sacilotto de Souza]

From: Alistair Strachan <astrachan at google.com>

BugLink: https://bugs.launchpad.net/bugs/1830890

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.

See relevant bug reports for additional info:

  https://bugzilla.kernel.org/show_bug.cgi?id=201741
  https://bugzilla.redhat.com/show_bug.cgi?id=1659295

Fixes: 379d98ddf413 ("x86: vdso: Use $LD instead of $CC to link")
Reported-by: Florian Weimer <fweimer at redhat.com>
Reported-by: Carlos O'Donell <carlos at redhat.com>
Reported-by: "H. J. Lu" <hjl.tools at gmail.com>
Signed-off-by: Alistair Strachan <astrachan at google.com>
Signed-off-by: Borislav Petkov <bp at suse.de>
Tested-by: Laura Abbott <labbott at redhat.com>
Cc: Andy Lutomirski <luto at kernel.org>
Cc: Carlos O'Donell <carlos at redhat.com>
Cc: "H. Peter Anvin" <hpa at zytor.com>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: Joel Fernandes <joel at joelfernandes.org>
Cc: kernel-team at android.com
Cc: Laura Abbott <labbott at redhat.com>
Cc: stable <stable at vger.kernel.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: X86 ML <x86 at kernel.org>
Link: https://lkml.kernel.org/r/20181214223637.35954-1-astrachan@google.com
(cherry picked from commit cd01544a268ad8ee5b1dfe42c4393f1095f86879)
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
---
 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 297dda4d5947..15ed35f5097d 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -159,7 +159,8 @@ 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
 
 #
-- 
2.17.1