kselftest/arm64: bti: force static linking

[PATCH] kselftest/arm64: bti: force static linking

Posted by Andre Przywara 3 years, 12 months ago

The "bti" selftests are built with -nostdlib, which apparently
automatically creates a statically linked binary, which is what we want
and need for BTI (to avoid interactions with the dynamic linker).

However this is not true when building a PIE binary, which some
toolchains (Ubuntu) configure as the default.
When compiling btitest with such a toolchain, it will create a
dynamically linked binary, which will probably fail some tests, as the
dynamic linker might not support BTI:
===================
TAP version 13
1..18
not ok 1 nohint_func/call_using_br_x0
not ok 2 nohint_func/call_using_br_x16
not ok 3 nohint_func/call_using_blr
....
===================

To make sure we create static binaries, add an explicit -static on the
linker command line. This forces static linking even if the toolchain
defaults to PIE builds, and fixes btitest runs on BTI enabled machines.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 tools/testing/selftests/arm64/bti/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/arm64/bti/Makefile b/tools/testing/selftests/arm64/bti/Makefile
index 73e013c082a65..dafa1c2aa5c47 100644
--- a/tools/testing/selftests/arm64/bti/Makefile
+++ b/tools/testing/selftests/arm64/bti/Makefile
@@ -39,7 +39,7 @@ BTI_OBJS =                                      \
 	teststubs-bti.o                         \
 	trampoline-bti.o
 gen/btitest: $(BTI_OBJS)
-	$(CC) $(CFLAGS_BTI) $(CFLAGS_COMMON) -nostdlib -o $@ $^
+	$(CC) $(CFLAGS_BTI) $(CFLAGS_COMMON) -nostdlib -static -o $@ $^
 
 NOBTI_OBJS =                                    \
 	test-nobti.o                         \
@@ -50,7 +50,7 @@ NOBTI_OBJS =                                    \
 	teststubs-nobti.o                       \
 	trampoline-nobti.o
 gen/nobtitest: $(NOBTI_OBJS)
-	$(CC) $(CFLAGS_BTI) $(CFLAGS_COMMON) -nostdlib -o $@ $^
+	$(CC) $(CFLAGS_BTI) $(CFLAGS_COMMON) -nostdlib -static -o $@ $^
 
 # Including KSFT lib.mk here will also mangle the TEST_GEN_PROGS list
 # to account for any OUTPUT target-dirs optionally provided by
-- 
2.25.1

Re: [PATCH] kselftest/arm64: bti: force static linking

Posted by Catalin Marinas 3 years, 11 months ago

On Wed, 11 May 2022 18:21:29 +0100, Andre Przywara wrote:
> The "bti" selftests are built with -nostdlib, which apparently
> automatically creates a statically linked binary, which is what we want
> and need for BTI (to avoid interactions with the dynamic linker).
> 
> However this is not true when building a PIE binary, which some
> toolchains (Ubuntu) configure as the default.
> When compiling btitest with such a toolchain, it will create a
> dynamically linked binary, which will probably fail some tests, as the
> dynamic linker might not support BTI:
> ===================
> TAP version 13
> 1..18
> not ok 1 nohint_func/call_using_br_x0
> not ok 2 nohint_func/call_using_br_x16
> not ok 3 nohint_func/call_using_blr
> ....
> ===================
> 
> [...]

Applied to arm64 (for-next/kselftest), thanks!

[1/1] kselftest/arm64: bti: force static linking
      https://git.kernel.org/arm64/c/d7a49291d786

-- 
Catalin

Re: [PATCH] kselftest/arm64: bti: force static linking

Posted by Catalin Marinas 3 years, 11 months ago

On Wed, May 11, 2022 at 06:21:29PM +0100, Andre Przywara wrote:
> The "bti" selftests are built with -nostdlib, which apparently
> automatically creates a statically linked binary, which is what we want
> and need for BTI (to avoid interactions with the dynamic linker).
> 
> However this is not true when building a PIE binary, which some
> toolchains (Ubuntu) configure as the default.
> When compiling btitest with such a toolchain, it will create a
> dynamically linked binary, which will probably fail some tests, as the
> dynamic linker might not support BTI:
> ===================
> TAP version 13
> 1..18
> not ok 1 nohint_func/call_using_br_x0
> not ok 2 nohint_func/call_using_br_x16
> not ok 3 nohint_func/call_using_blr
> ....
> ===================
> 
> To make sure we create static binaries, add an explicit -static on the
> linker command line. This forces static linking even if the toolchain
> defaults to PIE builds, and fixes btitest runs on BTI enabled machines.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>

Does this need to go in as a fix (cc stable, fixes tag)?

-- 
Catalin

Re: [PATCH] kselftest/arm64: bti: force static linking

Posted by Andre Przywara 3 years, 11 months ago

On Sun, 15 May 2022 11:05:23 +0100
Catalin Marinas <catalin.marinas@arm.com> wrote:

Hi,

> On Wed, May 11, 2022 at 06:21:29PM +0100, Andre Przywara wrote:
> > The "bti" selftests are built with -nostdlib, which apparently
> > automatically creates a statically linked binary, which is what we want
> > and need for BTI (to avoid interactions with the dynamic linker).
> > 
> > However this is not true when building a PIE binary, which some
> > toolchains (Ubuntu) configure as the default.
> > When compiling btitest with such a toolchain, it will create a
> > dynamically linked binary, which will probably fail some tests, as the
> > dynamic linker might not support BTI:
> > ===================
> > TAP version 13
> > 1..18
> > not ok 1 nohint_func/call_using_br_x0
> > not ok 2 nohint_func/call_using_br_x16
> > not ok 3 nohint_func/call_using_blr
> > ....
> > ===================
> > 
> > To make sure we create static binaries, add an explicit -static on the
> > linker command line. This forces static linking even if the toolchain
> > defaults to PIE builds, and fixes btitest runs on BTI enabled machines.
> > 
> > Signed-off-by: Andre Przywara <andre.przywara@arm.com>  
> 
> Does this need to go in as a fix (cc stable, fixes tag)?

I dimly remember some discussion about stable fixes not being a real thing
for the selftests? In any case:

Fixes: 314bcbf09f14 ("kselftest: arm64: Add BTI tests")

Cheers,
Andre

Re: [PATCH] kselftest/arm64: bti: force static linking

Posted by Catalin Marinas 3 years, 11 months ago

On Mon, May 16, 2022 at 10:29:35AM +0100, Andre Przywara wrote:
> On Sun, 15 May 2022 11:05:23 +0100
> Catalin Marinas <catalin.marinas@arm.com> wrote:
> > On Wed, May 11, 2022 at 06:21:29PM +0100, Andre Przywara wrote:
> > > The "bti" selftests are built with -nostdlib, which apparently
> > > automatically creates a statically linked binary, which is what we want
> > > and need for BTI (to avoid interactions with the dynamic linker).
> > > 
> > > However this is not true when building a PIE binary, which some
> > > toolchains (Ubuntu) configure as the default.
> > > When compiling btitest with such a toolchain, it will create a
> > > dynamically linked binary, which will probably fail some tests, as the
> > > dynamic linker might not support BTI:
> > > ===================
> > > TAP version 13
> > > 1..18
> > > not ok 1 nohint_func/call_using_br_x0
> > > not ok 2 nohint_func/call_using_br_x16
> > > not ok 3 nohint_func/call_using_blr
> > > ....
> > > ===================
> > > 
> > > To make sure we create static binaries, add an explicit -static on the
> > > linker command line. This forces static linking even if the toolchain
> > > defaults to PIE builds, and fixes btitest runs on BTI enabled machines.
> > > 
> > > Signed-off-by: Andre Przywara <andre.przywara@arm.com>  
> > 
> > Does this need to go in as a fix (cc stable, fixes tag)?
> 
> I dimly remember some discussion about stable fixes not being a real thing
> for the selftests? In any case:
> 
> Fixes: 314bcbf09f14 ("kselftest: arm64: Add BTI tests")

I'll add the fixes tag. I can see the occasional cc stable for kselftest
patches.

-- 
Catalin

Re: [PATCH] kselftest/arm64: bti: force static linking

Posted by Mark Brown 3 years, 12 months ago

On Wed, May 11, 2022 at 06:21:29PM +0100, Andre Przywara wrote:
> The "bti" selftests are built with -nostdlib, which apparently
> automatically creates a statically linked binary, which is what we want
> and need for BTI (to avoid interactions with the dynamic linker).

Reviewed-by: Mark Brown <broonie@kernel.org>