This test case is used to produce the bug that:
KVM may turn a user page to a kernel page when kernel writes a readonly
user page if CR0.WP = 1. This shadow page entry will be reused after
SMAP is enabled so that kernel is allowed to access this user page
Signed-off-by: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
---
x86/smap.c | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/x86/smap.c b/x86/smap.c
index 042c5aa..66f97b8 100644
--- a/x86/smap.c
+++ b/x86/smap.c
@@ -48,6 +48,7 @@ asm ("pf_tss:\n"
#define USER_BASE (1 << 24)
#define USER_VAR(v) (*((__typeof__(&(v))) (((unsigned long)&v) + USER_BASE)))
+#define USER_ADDR(v) ((void *)((unsigned long)(&v) + USER_BASE))
static void init_test(int i)
{
@@ -58,6 +59,29 @@ static void init_test(int i)
}
}
+static void check_smap_nowp(void)
+{
+ test = 0x99;
+
+ *get_pte(phys_to_virt(read_cr3()), USER_ADDR(test)) &= ~PTE_WRITE;
+
+ write_cr4(read_cr4() & ~X86_CR4_SMAP);
+ write_cr0(read_cr0() & ~X86_CR0_WP);
+ clac();
+ write_cr3(read_cr3());
+
+ init_test(0);
+ USER_VAR(test) = 0x99;
+ report("write from user page with SMAP=0, AC=0, WP=0, PTE.U=1 && PTE.W=0", pf_count == 0);
+
+ write_cr4(read_cr4() | X86_CR4_SMAP);
+ write_cr3(read_cr3());
+
+ init_test(0);
+ (void)USER_VAR(test);
+ report("read from user page with SMAP=1, AC=0, WP=0, PTE.U=1 && PTE.W=0", pf_count == 1 && save == 0x99);
+}
+
int main(int ac, char **av)
{
unsigned long i;
@@ -150,6 +174,8 @@ int main(int ac, char **av)
report("executing on user page with AC=0", pf_count == 0);
}
+ check_smap_nowp();
+
// TODO: implicit kernel access from ring 3 (e.g. int)
return report_summary();
--
2.1.0
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
