From: Zixuan Wang <zixuanwang@xxxxxxxxxx>
UEFI sets up page tables before executing EFI application binaries.
These page tables do not allow user space code to access kernel space
memory. But `x86/syscall.c` test case places a user space function
`syscall_tf_user32` inside kernel space memory. When using UEFI page
tables, fetching this kernel memory from user space triggers a #PF
fault, which is not expected by this test case.
KVM-Unit-Tests defines page tables that allow such behavior. So the
solution to this problem is to load KVM-Unit-Tests' page tables:
1. Copy the page table definition from `x86/cstart64.S`
2. Update page table entries with runtime memory addresses
3. Update CR3 register with the new page table root address
Since this commit, `x86/syscall.c` can run in UEFI and generate same
output as in Seabios, using the following command:
./x86/efi/run ./x86/syscall.efi --cpu Opteron_G1,vendor=AuthenticAMD
Signed-off-by: Zixuan Wang <zixuanwang@xxxxxxxxxx>
---
lib/x86/asm/page.h | 1 +
lib/x86/asm/setup.h | 3 +++
lib/x86/setup.c | 55 ++++++++++++++++++++++++++++++++++++++++++++
x86/efi/efistart64.S | 23 ++++++++++++++++++
4 files changed, 82 insertions(+)
diff --git a/lib/x86/asm/page.h b/lib/x86/asm/page.h
index fc14160..f6f740b 100644
--- a/lib/x86/asm/page.h
+++ b/lib/x86/asm/page.h
@@ -31,6 +31,7 @@ typedef unsigned long pgd_t;
#define PT_ACCESSED_MASK (1ull << 5)
#define PT_DIRTY_MASK (1ull << 6)
#define PT_PAGE_SIZE_MASK (1ull << 7)
+#define PT_GLOBAL_MASK (1ull << 8)
#define PT64_NX_MASK (1ull << 63)
#define PT_ADDR_MASK GENMASK_ULL(51, 12)
diff --git a/lib/x86/asm/setup.h b/lib/x86/asm/setup.h
index ecfcd5c..9cc135a 100644
--- a/lib/x86/asm/setup.h
+++ b/lib/x86/asm/setup.h
@@ -8,7 +8,9 @@ unsigned long setup_tss(void);
#ifdef TARGET_EFI
#include "x86/acpi.h"
#include "x86/apic.h"
+#include "x86/processor.h"
#include "x86/smp.h"
+#include "asm/page.h"
#include "efi.h"
/*
@@ -26,6 +28,7 @@ typedef struct {
void setup_efi_bootinfo(efi_bootinfo_t *efi_bootinfo);
void setup_efi(efi_bootinfo_t *efi_bootinfo);
efi_status_t setup_efi_pre_boot(unsigned long *mapkey, efi_bootinfo_t *efi_bootinfo);
+void setup_5level_page_table(void);
#endif /* TARGET_EFI */
#endif /* _X86_ASM_SETUP_H_ */
diff --git a/lib/x86/setup.c b/lib/x86/setup.c
index 6d81ab6..c1aa82a 100644
--- a/lib/x86/setup.c
+++ b/lib/x86/setup.c
@@ -254,6 +254,60 @@ efi_status_t setup_efi_pre_boot(unsigned long *mapkey, efi_bootinfo_t *efi_booti
return EFI_SUCCESS;
}
+/* Defined in cstart64.S or efistart64.S */
+extern phys_addr_t ptl5;
+extern phys_addr_t ptl4;
+extern phys_addr_t ptl3;
+extern phys_addr_t ptl2;
+
+static void setup_page_table(void)
+{
+ pgd_t *curr_pt;
+ phys_addr_t flags;
+ int i;
+
+ /* Set default flags */
+ flags = PT_PRESENT_MASK | PT_WRITABLE_MASK | PT_USER_MASK;
+
+ /* Level 5 */
+ curr_pt = (pgd_t *)&ptl5;
+ curr_pt[0] = ((phys_addr_t)&ptl4) | flags;
+ /* Level 4 */
+ curr_pt = (pgd_t *)&ptl4;
+ curr_pt[0] = ((phys_addr_t)&ptl3) | flags;
+ /* Level 3 */
+ curr_pt = (pgd_t *)&ptl3;
+ for (i = 0; i < 4; i++) {
+ curr_pt[i] = (((phys_addr_t)&ptl2) + i * PAGE_SIZE) | flags;
+ }
+ /* Level 2 */
+ curr_pt = (pgd_t *)&ptl2;
+ flags |= PT_ACCESSED_MASK | PT_DIRTY_MASK | PT_PAGE_SIZE_MASK | PT_GLOBAL_MASK;
+ for (i = 0; i < 4 * 512; i++) {
+ curr_pt[i] = ((phys_addr_t)(i << 21)) | flags;
+ }
+
+ /* Load 4-level page table */
+ write_cr3((ulong)&ptl4);
+}
+
+void setup_5level_page_table(void)
+{
+ /*
+ * TODO: This function is a place holder for now. It is defined because
+ * some test cases (e.g. x86/access.c) expect it to exist. If this
+ * function is not defined, gcc may generate wrong position-independent
+ * code, which leads to incorrect memory access: if compiling
+ * x86/access.efi without this function defined, several data structures
+ * (e.g. apic_ops) get compile time offset memory addresses, but they
+ * should get runtime %rip based addresses.
+ *
+ * The reason this function does not contain any code: Setting up 5
+ * level page table requires x86 to enter the real mode. But real mode
+ * is currently not supported in kvm-unit-tests under UEFI.
+ */
+}
+
static void setup_gdt_tss(void)
{
size_t tss_offset;
@@ -274,6 +328,7 @@ void setup_efi(efi_bootinfo_t *efi_bootinfo)
smp_init();
phys_alloc_init(efi_bootinfo->free_mem_start, efi_bootinfo->free_mem_size);
setup_efi_rsdp(efi_bootinfo->rsdp);
+ setup_page_table();
}
#endif /* TARGET_EFI */
diff --git a/x86/efi/efistart64.S b/x86/efi/efistart64.S
index 57299a5..adfff3a 100644
--- a/x86/efi/efistart64.S
+++ b/x86/efi/efistart64.S
@@ -17,6 +17,29 @@ ring0stacksize = PAGE_SIZE
.align 16
ring0stacktop:
+.data
+
+.align PAGE_SIZE
+.globl ptl2
+ptl2:
+ . = . + 4 * PAGE_SIZE
+.align PAGE_SIZE
+
+.globl ptl3
+ptl3:
+ . = . + PAGE_SIZE
+.align PAGE_SIZE
+
+.globl ptl4
+ptl4:
+ . = . + PAGE_SIZE
+.align PAGE_SIZE
+
+.globl ptl5
+ptl5:
+ . = . + PAGE_SIZE
+.align PAGE_SIZE
+
.section .init
.code64
.text
--
2.33.0
