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

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

[Alistair Strachan]

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: Laura Abbott <labbott@redhat.com>
Fixes: 379d98ddf413 ("x86: vdso: Use $LD instead of $CC to link")
Cc: stable@vger.kernel.org
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: X86 ML <x86@kernel.org>
Cc: Florian Weimer <fweimer@redhat.com>,
Cc: Carlos O'Donell <carlos@redhat.com>,
Cc: "H. J. Lu" <hjl.tools@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: kernel-team@android.com
Signed-off-by: Alistair Strachan <astrachan@google.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 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

Re: [PATCH] x86: vdso: Pass --eh-frame-hdr to ld

[Laura Abbott]

On 12/14/18 2:27 PM, Alistair Strachan wrote:
> 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: Laura Abbott <labbott@redhat.com>

You should probably use the bugzilla reporters instead
of me given I just did the boring part of sending an e-mail.
Instead you can use:

Tested-by: Laura Abbott <labbott@redhat.com>

> Fixes: 379d98ddf413 ("x86: vdso: Use $LD instead of $CC to link")
> Cc: stable@vger.kernel.org
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: X86 ML <x86@kernel.org>
> Cc: Florian Weimer <fweimer@redhat.com>,
> Cc: Carlos O'Donell <carlos@redhat.com>,
> Cc: "H. J. Lu" <hjl.tools@gmail.com>
> Cc: Joel Fernandes <joel@joelfernandes.org>
> Cc: kernel-team@android.com
> Signed-off-by: Alistair Strachan <astrachan@google.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 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
>   
>   #
>