linux-kernel - [PATCH] lkdtm/bugs: Avoid ifdefs for DOUBLE

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Date:   Wed, 27 Nov 2019 11:19:20 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>, x86 <x86@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] lkdtm/bugs: Avoid ifdefs for DOUBLE_FAULT

LKDTM test visibility shouldn't change, so remove the ifdefs on
DOUBLE_FAULT and make sure test failure doesn't crash the system.

Link: https://lore.kernel.org/lkml/20191127184837.GA35982@gmail.com
Fixes: b09511c253e5 ("lkdtm: Add a DOUBLE_FAULT crash type on x86")
Signed-off-by: Kees Cook <keescook@...omium.org>
---
applies on top of tip/x86/urgent
---
 drivers/misc/lkdtm/bugs.c  | 8 +++++---
 drivers/misc/lkdtm/core.c  | 4 +---
 drivers/misc/lkdtm/lkdtm.h | 2 --
 3 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index a4fdad04809a..22f5293414cc 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -342,9 +342,9 @@ void lkdtm_UNSET_SMEP(void)
 #endif
 }
 
-#ifdef CONFIG_X86_32
 void lkdtm_DOUBLE_FAULT(void)
 {
+#ifdef CONFIG_X86_32
 	/*
 	 * Trigger #DF by setting the stack limit to zero.  This clobbers
 	 * a GDT TLS slot, which is okay because the current task will die
@@ -373,6 +373,8 @@ void lkdtm_DOUBLE_FAULT(void)
 	asm volatile ("movw %0, %%ss; addl $0, (%%esp)" ::
 		      "r" ((unsigned short)(GDT_ENTRY_TLS_MIN << 3)));
 
-	panic("tried to double fault but didn't die\n");
-}
+	pr_err("FAIL: tried to double fault but didn't die!\n");
+#else
+	pr_err("FAIL: this test is only available on 32-bit x86.\n");
 #endif
+}
diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
index ee0d6e721441..7082ef8a2b99 100644
--- a/drivers/misc/lkdtm/core.c
+++ b/drivers/misc/lkdtm/core.c
@@ -116,6 +116,7 @@ static const struct crashtype crashtypes[] = {
 	CRASHTYPE(STACK_GUARD_PAGE_LEADING),
 	CRASHTYPE(STACK_GUARD_PAGE_TRAILING),
 	CRASHTYPE(UNSET_SMEP),
+	CRASHTYPE(DOUBLE_FAULT),
 	CRASHTYPE(UNALIGNED_LOAD_STORE_WRITE),
 	CRASHTYPE(OVERWRITE_ALLOCATION),
 	CRASHTYPE(WRITE_AFTER_FREE),
@@ -171,9 +172,6 @@ static const struct crashtype crashtypes[] = {
 	CRASHTYPE(USERCOPY_KERNEL_DS),
 	CRASHTYPE(STACKLEAK_ERASING),
 	CRASHTYPE(CFI_FORWARD_PROTO),
-#ifdef CONFIG_X86_32
-	CRASHTYPE(DOUBLE_FAULT),
-#endif
 };
 
 
diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
index c56d23e37643..f4952efd6785 100644
--- a/drivers/misc/lkdtm/lkdtm.h
+++ b/drivers/misc/lkdtm/lkdtm.h
@@ -28,9 +28,7 @@ void lkdtm_CORRUPT_USER_DS(void);
 void lkdtm_STACK_GUARD_PAGE_LEADING(void);
 void lkdtm_STACK_GUARD_PAGE_TRAILING(void);
 void lkdtm_UNSET_SMEP(void);
-#ifdef CONFIG_X86_32
 void lkdtm_DOUBLE_FAULT(void);
-#endif
 
 /* lkdtm_heap.c */
 void __init lkdtm_heap_init(void);
-- 
2.17.1


-- 
Kees Cook