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Subject[PATCH 3/3] lkdtm: add "WRITE_KERN" test
Date
Add "WRITE_KERN" crash target to validate that kernel executable memory
is not writable.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
drivers/misc/lkdtm.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)

diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c
index d6ee1aae3e72..d30301149242 100644
--- a/drivers/misc/lkdtm.c
+++ b/drivers/misc/lkdtm.c
@@ -102,6 +102,7 @@ enum ctype {
CT_EXEC_USERSPACE,
CT_ACCESS_USERSPACE,
CT_WRITE_RO,
+ CT_WRITE_KERN,
};

static char* cp_name[] = {
@@ -138,6 +139,7 @@ static char* cp_type[] = {
"EXEC_USERSPACE",
"ACCESS_USERSPACE",
"WRITE_RO",
+ "WRITE_KERN",
};

static struct jprobe lkdtm;
@@ -317,6 +319,13 @@ static void do_nothing(void)
return;
}

+/* Must immediately follow do_nothing for size calculuations to work out. */
+static void do_overwritten(void)
+{
+ pr_info("do_overwritten wasn't overwritten!\n");
+ return;
+}
+
static noinline void corrupt_stack(void)
{
/* Use default char array length that triggers stack protection. */
@@ -496,6 +505,22 @@ static void lkdtm_do_action(enum ctype which)

break;
}
+ case CT_WRITE_KERN: {
+ size_t size;
+ unsigned char *ptr;
+
+ size = (unsigned long)do_overwritten -
+ (unsigned long)do_nothing;
+ ptr = (unsigned char *)do_overwritten;
+
+ pr_info("attempting bad %zu byte write at %p\n", size, ptr);
+ memcpy(ptr, (unsigned char *)do_nothing, size);
+ flush_icache_range((unsigned long)ptr,
+ (unsigned long)(ptr + size));
+
+ do_overwritten();
+ break;
+ }
case CT_NONE:
default:
break;
--
1.7.9.5


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