According to section "CR3" in APM vol. 2, the non-MBZ reserved bits in CR3
need to be set by software as follows:
"Reserved Bits. Reserved fields should be cleared to 0 by software
when writing CR3."
But experiments show that consistency checking in SVM ignores these
non-MBZ-reserved bits in CR3, meaning they can be set to 1 also. However,
setting them to 1 may cause guest crashes in some modes and in bare metal
environments. Hence, this test induces an #NPF by clearing the "P" bit in
the highest level page table, when testing the 1-setting of these bits.
Inducing an #NPF causes the guest to exit to userspace before any guest
instruction is executed thus avoiding any crash.
Signed-off-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>
---
x86/svm.h | 4 ++-
x86/svm_tests.c | 66 ++++++++++++++++++++++++++++++++++++++++++++-----
2 files changed, 63 insertions(+), 7 deletions(-)
diff --git a/x86/svm.h b/x86/svm.h
index 15e0f18..d657592 100644
--- a/x86/svm.h
+++ b/x86/svm.h
@@ -325,7 +325,9 @@ struct __attribute__ ((__packed__)) vmcb {
#define SVM_CR0_SELECTIVE_MASK (X86_CR0_TS | X86_CR0_MP)
#define SVM_CR0_RESERVED_MASK 0xffffffff00000000U
-#define SVM_CR3_LONG_RESERVED_MASK 0xfff0000000000000U
+#define SVM_CR3_LONG_MBZ_MASK 0xfff0000000000000U
+#define SVM_CR3_LONG_RESERVED_MASK 0x0000000000000fe7U
+#define SVM_CR3_PAE_LEGACY_RESERVED_MASK 0x0000000000000007U
#define SVM_CR4_LEGACY_RESERVED_MASK 0xff88f000U
#define SVM_CR4_RESERVED_MASK 0xffffffffff88f000U
#define SVM_DR6_RESERVED_MASK 0xffffffffffff1ff0U
diff --git a/x86/svm_tests.c b/x86/svm_tests.c
index 1908c7c..ed21d21 100644
--- a/x86/svm_tests.c
+++ b/x86/svm_tests.c
@@ -1913,7 +1913,8 @@ static void basic_guest_main(struct svm_test *test)
} \
}
-#define SVM_TEST_CR_RESERVED_BITS(start, end, inc, cr, val, resv_mask) \
+#define SVM_TEST_CR_RESERVED_BITS(start, end, inc, cr, val, resv_mask, \
+ exit_code) \
{ \
u64 tmp, mask; \
int i; \
@@ -1933,7 +1934,7 @@ static void basic_guest_main(struct svm_test *test)
case 4: \
vmcb->save.cr4 = tmp; \
} \
- report(svm_vmrun() == SVM_EXIT_ERR, "Test CR%d %d:%d: %lx",\
+ report(svm_vmrun() == exit_code, "Test CR%d %d:%d: %lx",\
cr, end, start, tmp); \
} \
}
@@ -2012,9 +2013,62 @@ static void test_cr3(void)
u64 cr3_saved = vmcb->save.cr3;
SVM_TEST_CR_RESERVED_BITS(0, 63, 1, 3, cr3_saved,
- SVM_CR3_LONG_RESERVED_MASK);
+ SVM_CR3_LONG_MBZ_MASK, SVM_EXIT_ERR);
+
+ vmcb->save.cr3 = cr3_saved & ~SVM_CR3_LONG_MBZ_MASK;
+ report(svm_vmrun() == SVM_EXIT_VMMCALL, "Test CR3 63:0: %lx",
+ vmcb->save.cr3);
+
+ /*
+ * CR3 non-MBZ reserved bits based on different modes:
+ * [11:5] [2:0] - long mode
+ * [2:0] - PAE legacy mode
+ */
+ u64 cr4_saved = vmcb->save.cr4;
+ u64 *pdpe = npt_get_pml4e();
+
+ /*
+ * Long mode
+ */
+ if (this_cpu_has(X86_FEATURE_PCID)) {
+ vmcb->save.cr4 = cr4_saved | X86_CR4_PCIDE;
+ SVM_TEST_CR_RESERVED_BITS(0, 11, 1, 3, cr3_saved,
+ SVM_CR3_LONG_RESERVED_MASK, SVM_EXIT_VMMCALL);
+
+ vmcb->save.cr3 = cr3_saved & ~SVM_CR3_LONG_RESERVED_MASK;
+ report(svm_vmrun() == SVM_EXIT_VMMCALL, "Test CR3 63:0: %lx",
+ vmcb->save.cr3);
+ } else {
+
+ vmcb->save.cr4 = cr4_saved & ~X86_CR4_PCIDE;
+
+ /* Clear P (Present) bit in NPT in order to trigger #NPF */
+ pdpe[0] &= ~1ULL;
+
+ SVM_TEST_CR_RESERVED_BITS(0, 11, 1, 3, cr3_saved,
+ SVM_CR3_LONG_RESERVED_MASK, SVM_EXIT_NPF);
+
+ pdpe[0] |= 1ULL;
+ vmcb->save.cr3 = cr3_saved & ~SVM_CR3_LONG_RESERVED_MASK;
+ report(svm_vmrun() == SVM_EXIT_VMMCALL, "Test CR3 63:0: %lx",
+ vmcb->save.cr3);
+ }
+
+ /*
+ * PAE legacy
+ */
+ pdpe[0] &= ~1ULL;
+ vmcb->save.cr4 = cr4_saved | X86_CR4_PAE;
+ SVM_TEST_CR_RESERVED_BITS(0, 2, 1, 3, cr3_saved,
+ SVM_CR3_PAE_LEGACY_RESERVED_MASK, SVM_EXIT_NPF);
+
+ pdpe[0] |= 1ULL;
+ vmcb->save.cr3 = cr3_saved & ~SVM_CR3_PAE_LEGACY_RESERVED_MASK;
+ report(svm_vmrun() == SVM_EXIT_VMMCALL, "Test CR3 63:0: %lx",
+ vmcb->save.cr3);
vmcb->save.cr3 = cr3_saved;
+ vmcb->save.cr4 = cr4_saved;
}
static void test_cr4(void)
@@ -2031,14 +2085,14 @@ static void test_cr4(void)
efer &= ~EFER_LME;
vmcb->save.efer = efer;
SVM_TEST_CR_RESERVED_BITS(12, 31, 1, 4, cr4_saved,
- SVM_CR4_LEGACY_RESERVED_MASK);
+ SVM_CR4_LEGACY_RESERVED_MASK, SVM_EXIT_ERR);
efer |= EFER_LME;
vmcb->save.efer = efer;
SVM_TEST_CR_RESERVED_BITS(12, 31, 1, 4, cr4_saved,
- SVM_CR4_RESERVED_MASK);
+ SVM_CR4_RESERVED_MASK, SVM_EXIT_ERR);
SVM_TEST_CR_RESERVED_BITS(32, 63, 4, 4, cr4_saved,
- SVM_CR4_RESERVED_MASK);
+ SVM_CR4_RESERVED_MASK, SVM_EXIT_ERR);
vmcb->save.cr4 = cr4_saved;
vmcb->save.efer = efer_saved;
--
2.18.4
