[RFC,v4,03/12] selftests: x86/sgx: Mark the enclave loader as not needing an exec stack
diff mbox series

Message ID 20190619222401.14942-4-sean.j.christopherson@intel.com
State New
Headers show
Series
  • security: x86/sgx: SGX vs. LSM
Related show

Commit Message

Sean Christopherson June 19, 2019, 10:23 p.m. UTC
The SGX enclave loader doesn't need an executable stack, but linkers
will assume it does due to the lack of .note.GNU-stack sections in the
loader's assembly code.  As a result, the kernel tags the loader as
having "read implies exec", and so adds PROT_EXEC to all mmap()s, even
those for mapping EPC regions.  This will cause problems in the future
when userspace needs to explicit state a page's protection bits when the
page is added to an enclave, e.g. adding TCS pages as R+W will cause
mmap() to fail when the kernel tacks on +X.

Explicitly tell the linker that an executable stack is not needed.
Alternatively, each .S file could add .note.GNU-stack, but the loader
should never need an executable stack so zap it in one fell swoop.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 tools/testing/selftests/x86/sgx/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Jarkko Sakkinen June 20, 2019, 9:17 p.m. UTC | #1
On Wed, Jun 19, 2019 at 03:23:52PM -0700, Sean Christopherson wrote:
> The SGX enclave loader doesn't need an executable stack, but linkers
> will assume it does due to the lack of .note.GNU-stack sections in the
> loader's assembly code.  As a result, the kernel tags the loader as
> having "read implies exec", and so adds PROT_EXEC to all mmap()s, even
> those for mapping EPC regions.  This will cause problems in the future
> when userspace needs to explicit state a page's protection bits when the
> page is added to an enclave, e.g. adding TCS pages as R+W will cause
> mmap() to fail when the kernel tacks on +X.
> 
> Explicitly tell the linker that an executable stack is not needed.
> Alternatively, each .S file could add .note.GNU-stack, but the loader
> should never need an executable stack so zap it in one fell swoop.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>

OK, this one is squashed now. Thanks.

/Jarkko

Patch
diff mbox series

diff --git a/tools/testing/selftests/x86/sgx/Makefile b/tools/testing/selftests/x86/sgx/Makefile
index 1fd6f2708e81..10136b73096b 100644
--- a/tools/testing/selftests/x86/sgx/Makefile
+++ b/tools/testing/selftests/x86/sgx/Makefile
@@ -2,7 +2,7 @@  top_srcdir = ../../../../..
 
 include ../../lib.mk
 
-HOST_CFLAGS := -Wall -Werror -g $(INCLUDES) -fPIC
+HOST_CFLAGS := -Wall -Werror -g $(INCLUDES) -fPIC -z noexecstack
 ENCL_CFLAGS := -Wall -Werror -static -nostdlib -nostartfiles -fPIC \
 	       -fno-stack-protector -mrdrnd $(INCLUDES)