The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: b09511c253e5c739a60952b97c071a93e92b2e88
Gitweb: https://git.kernel.org/tip/b09511c253e5c739a60952b97c071a93e92b2e88
Author: Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Sun, 24 Nov 2019 21:18:04 -08:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 26 Nov 2019 21:53:34 +01:00
lkdtm: Add a DOUBLE_FAULT crash type on x86
The DOUBLE_FAULT crash does INT $8, which is a decent approximation
of a double fault. This is useful for testing the double fault
handling. Use it like:
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
drivers/misc/lkdtm/bugs.c | 39 +++++++++++++++++++++++++++++++++++++-
drivers/misc/lkdtm/core.c | 3 +++-
drivers/misc/lkdtm/lkdtm.h | 3 +++-
3 files changed, 45 insertions(+)
diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index 7284a22..a4fdad0 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -12,6 +12,10 @@
#include <linux/sched/task_stack.h>
#include <linux/uaccess.h>
+#ifdef CONFIG_X86_32
+#include <asm/desc.h>
+#endif
+
struct lkdtm_list {
struct list_head node;
};
@@ -337,3 +341,38 @@ void lkdtm_UNSET_SMEP(void)
pr_err("FAIL: this test is x86_64-only\n");
#endif
}
+
+#ifdef CONFIG_X86_32
+void lkdtm_DOUBLE_FAULT(void)
+{
+ /*
+ * Trigger #DF by setting the stack limit to zero. This clobbers
+ * a GDT TLS slot, which is okay because the current task will die
+ * anyway due to the double fault.
+ */
+ struct desc_struct d = {
+ .type = 3, /* expand-up, writable, accessed data */
+ .p = 1, /* present */
+ .d = 1, /* 32-bit */
+ .g = 0, /* limit in bytes */
+ .s = 1, /* not system */
+ };
+
+ local_irq_disable();
+ write_gdt_entry(get_cpu_gdt_rw(smp_processor_id()),
+ GDT_ENTRY_TLS_MIN, &d, DESCTYPE_S);
+
+ /*
+ * Put our zero-limit segment in SS and then trigger a fault. The
+ * 4-byte access to (%esp) will fault with #SS, and the attempt to
+ * deliver the fault will recursively cause #SS and result in #DF.
+ * This whole process happens while NMIs and MCEs are blocked by the
+ * MOV SS window. This is nice because an NMI with an invalid SS
+ * would also double-fault, resulting in the NMI or MCE being lost.
+ */
+ 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");
+}
+#endif
diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
index cbc4c90..ee0d6e7 100644
--- a/drivers/misc/lkdtm/core.c
+++ b/drivers/misc/lkdtm/core.c
@@ -171,6 +171,9 @@ 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 ab446e0..c56d23e 100644
--- a/drivers/misc/lkdtm/lkdtm.h
+++ b/drivers/misc/lkdtm/lkdtm.h
@@ -28,6 +28,9 @@ 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);
|