[PATCH 0/2] selftests/x86: Minor fixes

[PATCH 0/2] selftests/x86: Minor fixes

[Andy Lutomirski]

Two bugs fixed.

Andy Lutomirski (2):
  selftests/x86/fsgsbase: Fix GS == 1, 2, and 3 tests
  selftests/x86: Add missing .note.GNU-stack sections

 tools/testing/selftests/x86/fsgsbase.c              | 12 ++++++++++--
 tools/testing/selftests/x86/raw_syscall_helper_32.S |  2 ++
 tools/testing/selftests/x86/thunks.S                |  2 ++
 3 files changed, 14 insertions(+), 2 deletions(-)

-- 
2.28.0

[PATCH 1/2] selftests/x86/fsgsbase: Fix GS == 1, 2, and 3 tests

[Andy Lutomirski]

Setting GS to 1, 2, or 3 causes a nonsensical part of the IRET
microcode to change GS back to zero on a return from kernel mode to
user mode.  The result is that these tests fail randomly depending
on when interrupts happen.  Detect when this happens and let the
test pass.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 tools/testing/selftests/x86/fsgsbase.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
index 7161cfc2e60b..8c780cce941d 100644
--- a/tools/testing/selftests/x86/fsgsbase.c
+++ b/tools/testing/selftests/x86/fsgsbase.c
@@ -392,8 +392,8 @@ static void set_gs_and_switch_to(unsigned long local,
 		local = read_base(GS);
 
 		/*
-		 * Signal delivery seems to mess up weird selectors.  Put it
-		 * back.
+		 * Signal delivery is quite likely to change a selector
+		 * of 1, 2, or 3 back to 0 due to IRET being defective.
 		 */
 		asm volatile ("mov %0, %%gs" : : "rm" (force_sel));
 	} else {
@@ -411,6 +411,14 @@ static void set_gs_and_switch_to(unsigned long local,
 	if (base == local && sel_pre_sched == sel_post_sched) {
 		printf("[OK]\tGS/BASE remained 0x%hx/0x%lx\n",
 		       sel_pre_sched, local);
+	} else if (base == local && sel_pre_sched >= 1 && sel_pre_sched <= 3 &&
+		   sel_post_sched == 0) {
+		/*
+		 * IRET is misdesigned and will squash selectors 1, 2, or 3
+		 * to zero.  Don't fail the test just because this happened.
+		 */
+		printf("[OK]\tGS/BASE changed from 0x%hx/0x%lx to 0x%hx/0x%lx because IRET is defective\n",
+		       sel_pre_sched, local, sel_post_sched, base);
 	} else {
 		nerrs++;
 		printf("[FAIL]\tGS/BASE changed from 0x%hx/0x%lx to 0x%hx/0x%lx\n",
-- 
2.28.0

[PATCH 2/2] selftests/x86: Add missing .note.GNU-stack sections

[Andy Lutomirski]

Several of the x86 selftests end up with executable stacks because
the asm was missing the annotation that says that they are modern
and don't need executable stacks.  Add the annotations.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 tools/testing/selftests/x86/raw_syscall_helper_32.S | 2 ++
 tools/testing/selftests/x86/thunks.S                | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/tools/testing/selftests/x86/raw_syscall_helper_32.S b/tools/testing/selftests/x86/raw_syscall_helper_32.S
index 94410fa2b5ed..a10d36afdca0 100644
--- a/tools/testing/selftests/x86/raw_syscall_helper_32.S
+++ b/tools/testing/selftests/x86/raw_syscall_helper_32.S
@@ -45,3 +45,5 @@ int80_and_ret:
 
 	.type int80_and_ret, @function
 	.size int80_and_ret, .-int80_and_ret
+
+.section .note.GNU-stack,"",%progbits
diff --git a/tools/testing/selftests/x86/thunks.S b/tools/testing/selftests/x86/thunks.S
index 1bb5d62c16a4..a2d47d8344d4 100644
--- a/tools/testing/selftests/x86/thunks.S
+++ b/tools/testing/selftests/x86/thunks.S
@@ -57,3 +57,5 @@ call32_from_64:
 	ret
 
 .size call32_from_64, .-call32_from_64
+
+.section .note.GNU-stack,"",%progbits
-- 
2.28.0

[tip: x86/misc] selftests/x86: Add missing .note.GNU-stack sections

[tip-bot2 for Andy Lutomirski]

The following commit has been merged into the x86/misc branch of tip:

Commit-ID:     aeaaf005da1de075929e56562dced4a58238efc4
Gitweb:        https://git.kernel.org/tip/aeaaf005da1de075929e56562dced4a58238efc4
Author:        Andy Lutomirski <luto@kernel.org>
AuthorDate:    Mon, 02 Nov 2020 11:51:11 -08:00
Committer:     Borislav Petkov <bp@suse.de>
CommitterDate: Tue, 24 Nov 2020 13:55:39 +01:00

selftests/x86: Add missing .note.GNU-stack sections

Several of the x86 selftests end up with executable stacks because
the asm was missing the annotation that says that they are modern
and don't need executable stacks.  Add the annotations.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/6f043c03e9e0e4557e1e975a63b07a4d18965a68.1604346596.git.luto@kernel.org
---
 tools/testing/selftests/x86/raw_syscall_helper_32.S | 2 ++
 tools/testing/selftests/x86/thunks.S                | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/tools/testing/selftests/x86/raw_syscall_helper_32.S b/tools/testing/selftests/x86/raw_syscall_helper_32.S
index 94410fa..a10d36a 100644
--- a/tools/testing/selftests/x86/raw_syscall_helper_32.S
+++ b/tools/testing/selftests/x86/raw_syscall_helper_32.S
@@ -45,3 +45,5 @@ int80_and_ret:
 
 	.type int80_and_ret, @function
 	.size int80_and_ret, .-int80_and_ret
+
+.section .note.GNU-stack,"",%progbits
diff --git a/tools/testing/selftests/x86/thunks.S b/tools/testing/selftests/x86/thunks.S
index 1bb5d62..a2d47d8 100644
--- a/tools/testing/selftests/x86/thunks.S
+++ b/tools/testing/selftests/x86/thunks.S
@@ -57,3 +57,5 @@ call32_from_64:
 	ret
 
 .size call32_from_64, .-call32_from_64
+
+.section .note.GNU-stack,"",%progbits

[tip: x86/misc] selftests/x86/fsgsbase: Fix GS == 1, 2, and 3 tests

[tip-bot2 for Andy Lutomirski]

The following commit has been merged into the x86/misc branch of tip:

Commit-ID:     716572b0003ef67a4889bd7d85baf5099c5a0248
Gitweb:        https://git.kernel.org/tip/716572b0003ef67a4889bd7d85baf5099c5a0248
Author:        Andy Lutomirski <luto@kernel.org>
AuthorDate:    Mon, 02 Nov 2020 11:51:10 -08:00
Committer:     Borislav Petkov <bp@suse.de>
CommitterDate: Tue, 24 Nov 2020 13:46:16 +01:00

selftests/x86/fsgsbase: Fix GS == 1, 2, and 3 tests

Setting GS to 1, 2, or 3 causes a nonsensical part of the IRET microcode
to change GS back to zero on a return from kernel mode to user mode. The
result is that these tests fail randomly depending on when interrupts
happen. Detect when this happens and let the test pass.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/7567fd44a1d60a9424f25b19a998f12149993b0d.1604346596.git.luto@kernel.org
---
 tools/testing/selftests/x86/fsgsbase.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
index 7161cfc..8c780cc 100644
--- a/tools/testing/selftests/x86/fsgsbase.c
+++ b/tools/testing/selftests/x86/fsgsbase.c
@@ -392,8 +392,8 @@ static void set_gs_and_switch_to(unsigned long local,
 		local = read_base(GS);
 
 		/*
-		 * Signal delivery seems to mess up weird selectors.  Put it
-		 * back.
+		 * Signal delivery is quite likely to change a selector
+		 * of 1, 2, or 3 back to 0 due to IRET being defective.
 		 */
 		asm volatile ("mov %0, %%gs" : : "rm" (force_sel));
 	} else {
@@ -411,6 +411,14 @@ static void set_gs_and_switch_to(unsigned long local,
 	if (base == local && sel_pre_sched == sel_post_sched) {
 		printf("[OK]\tGS/BASE remained 0x%hx/0x%lx\n",
 		       sel_pre_sched, local);
+	} else if (base == local && sel_pre_sched >= 1 && sel_pre_sched <= 3 &&
+		   sel_post_sched == 0) {
+		/*
+		 * IRET is misdesigned and will squash selectors 1, 2, or 3
+		 * to zero.  Don't fail the test just because this happened.
+		 */
+		printf("[OK]\tGS/BASE changed from 0x%hx/0x%lx to 0x%hx/0x%lx because IRET is defective\n",
+		       sel_pre_sched, local, sel_post_sched, base);
 	} else {
 		nerrs++;
 		printf("[FAIL]\tGS/BASE changed from 0x%hx/0x%lx to 0x%hx/0x%lx\n",