Patch "selftests/x86: Add tests for the STR and SLDT instructions" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

selftests/x86: Add tests for the STR and SLDT instructions

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
selftests-x86-add-tests-for-the-str-and-sldt-instructions.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ricardo Neri <[email protected]>
Date: Sun, 5 Nov 2017 18:27:57 -0800
Subject: selftests/x86: Add tests for the STR and SLDT instructions

From: Ricardo Neri <[email protected]>

commit a9e017d5619eb371460c8e516f4684def62bef3a upstream.

The STR and SLDT instructions are not valid when running on virtual-8086 mode and generate an invalid operand exception. These two instructions are protected by the Intel User-Mode Instruction Prevention (UMIP) security feature. In protected mode, if UMIP is enabled, these instructions generate a general protection fault if called from CPL > 0. Linux traps the general protection fault and emulates the instructions sgdt, sidt and smsw; but not str and sldt.

These tests are added to verify that the emulation code does not emulate these two instructions but the expected invalid operand exception is seen.

Tests fallback to exit with INT3 in case emulation does happen.

---
 tools/testing/selftests/x86/entry_from_vm86.c |   18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

@@ -111,6 +111,11 @@ asm (
 	"smsw %ax\n\t"
 	"mov %ax, (2080)\n\t"
 	"int3\n\t"
+	"vmcode_umip_str:\n\t"
+	"str %eax\n\t"
+	"vmcode_umip_sldt:\n\t"
+	"sldt %eax\n\t"
+	"int3\n\t"
 	".size vmcode, . - vmcode\n\t"
 	"end_vmcode:\n\t"
 	".code32\n\t"

@@ -119,7 +124,8 @@ asm (
 
 extern unsigned char vmcode[], end_vmcode[];
 extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[],
-	vmcode_sti[], vmcode_int3[], vmcode_int80[], vmcode_umip[];
+	vmcode_sti[], vmcode_int3[], vmcode_int80[], vmcode_umip[],
+	vmcode_umip_str[], vmcode_umip_sldt[];
 
 /* Returns false if the test was skipped. */
 static bool do_test(struct vm86plus_struct *v86, unsigned long eip,

@@ -226,6 +232,16 @@ void do_umip_tests(struct vm86plus_struc
 		printf("[FAIL]\tAll the results of SIDT should be the same.\n");
 	else
 		printf("[PASS]\tAll the results from SIDT are identical.\n");
+
+	sethandler(SIGILL, sighandler, 0);
+	do_test(vm86, vmcode_umip_str - vmcode, VM86_SIGNAL, 0,
+		"STR instruction");
+	clearhandler(SIGILL);
+
+	sethandler(SIGILL, sighandler, 0);
+	do_test(vm86, vmcode_umip_sldt - vmcode, VM86_SIGNAL, 0,
+		"SLDT instruction");
+	clearhandler(SIGILL);
 }
 
 int main(void)

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/selftests-x86-add-tests-for-the-str-and-sldt-instructions.patch queue-4.4/selftests-x86-add-tests-for-user-mode-instruction-prevention.patch