riscv: Sync efi page table's kernel mappings before switching

The EFI page table is initially created as a copy of the kernel page table.
With VMAP_STACK enabled, kernel stacks are allocated in the vmalloc area:
if the stack is allocated in a new PGD (one that was not present at the
moment of the efi page table creation or not synced in a previous vmalloc
fault), the kernel will take a trap when switching to the efi page table
when the vmalloc kernel stack is accessed, resulting in a kernel panic.

Fix that by updating the efi kernel mappings before switching to the efi
page table.
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Fixes: b91540d5 ("RISC-V: Add EFI runtime services")
Tested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20221121133303.1782246-1-alexghiti@rivosinc.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/efi.h

@@ -10,6 +10,7 @@
 #include <asm/mmu_context.h>
 #include <asm/ptrace.h>
 #include <asm/tlbflush.h>
+#include <asm/pgalloc.h>
 
 #ifdef CONFIG_EFI
 extern void efi_init(void);
@@ -20,7 +21,10 @@ extern void efi_init(void);
 int efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md);
 int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md);
 
-#define arch_efi_call_virt_setup()      efi_virtmap_load()
+#define arch_efi_call_virt_setup()      ({		\
+		sync_kernel_mappings(efi_mm.pgd);	\
+		efi_virtmap_load();			\
+	})
 #define arch_efi_call_virt_teardown()   efi_virtmap_unload()
 
 #define ARCH_EFI_IRQ_FLAGS_MASK (SR_IE | SR_SPIE)

arch/riscv/include/asm/pgalloc.h

@@ -127,6 +127,13 @@ static inline void p4d_free(struct mm_struct *mm, p4d_t *p4d)
 #define __p4d_free_tlb(tlb, p4d, addr)  p4d_free((tlb)->mm, p4d)
 #endif /* __PAGETABLE_PMD_FOLDED */
 
+static inline void sync_kernel_mappings(pgd_t *pgd)
+{
+	memcpy(pgd + USER_PTRS_PER_PGD,
+	       init_mm.pgd + USER_PTRS_PER_PGD,
+	       (PTRS_PER_PGD - USER_PTRS_PER_PGD) * sizeof(pgd_t));
+}
+
 static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {
 	pgd_t *pgd;
@@ -135,9 +142,7 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 	if (likely(pgd != NULL)) {
 		memset(pgd, 0, USER_PTRS_PER_PGD * sizeof(pgd_t));
 		/* Copy kernel mappings */
-		memcpy(pgd + USER_PTRS_PER_PGD,
-			init_mm.pgd + USER_PTRS_PER_PGD,
-			(PTRS_PER_PGD - USER_PTRS_PER_PGD) * sizeof(pgd_t));
+		sync_kernel_mappings(pgd);
 	}
 	return pgd;
 }