linux-kernel - [PATCH v2] selftests/x86: Disable ldt_gdt

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Date:	Mon, 11 Jan 2016 17:23:32 -0800
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org
Cc:	Borislav Petkov <bp@...en8.de>,
	Shuah Khan <shuahkh@....samsung.com>,
	linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v2] selftests/x86: Disable ldt_gdt_64 for now

ldt_gdt.c relies on cross-cpu invalidation of SS to do one of its
tests.  On 32-bit builds, this works fine, but on 64-bit builds, it
only works if the kernel has proper SS sigcontext handling for
64-bit user programs.

Since the SS fixes are currently reverted, restrict the test case to
32 bits for now.

In principle, I could change the test to use a different segment
register, but it would be messy: CS can't point to the LDT for
64-bit code, and the other registers don't result in immediate
faults because they aren't reloaded on kernel -> user transitions.

When we fix sigcontext (in 4.6?), we can revert this.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---

Changes from v1: based on tip:x86/asm

tools/testing/selftests/x86/Makefile | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index eabcff411984..398bb0e6e38c 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -4,9 +4,10 @@ include ../lib.mk

 .PHONY: all all_32 all_64 warn_32bit_failure clean

-TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs ldt_gdt syscall_nt ptrace_syscall
+TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt ptrace_syscall
 TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault sigreturn test_syscall_vdso unwind_vdso \
-			test_FCMOV test_FCOMI test_FISTTP
+			test_FCMOV test_FCOMI test_FISTTP \
+			ldt_gdt

 TARGETS_C_32BIT_ALL := $(TARGETS_C_BOTHBITS) $(TARGETS_C_32BIT_ONLY)
 BINARIES_32 := $(TARGETS_C_32BIT_ALL:%=%_32)
-- 
2.5.0