Hi Alexandre,
On Mon, 21 Nov 2022 at 14:33, Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxx>
Thanks for the patch! With this applied on the Ubuntu 5.19 kernel I
can enable CONFIG_VMAP_STACK and cat /sys/firmware/efi/efivars/* on
the Unmatched without locking up. So
Tested-by: Emil Renner Berthing <emil.renner.berthing@xxxxxxxxxxxxx>
> ---
> arch/riscv/include/asm/efi.h | 6 +++++-
> arch/riscv/include/asm/pgalloc.h | 11 ++++++++---
> 2 files changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/arch/riscv/include/asm/efi.h b/arch/riscv/include/asm/efi.h
> index f74879a8f1ea..e229d7be4b66 100644
> --- a/arch/riscv/include/asm/efi.h
> +++ b/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)
> diff --git a/arch/riscv/include/asm/pgalloc.h b/arch/riscv/include/asm/pgalloc.h
> index 947f23d7b6af..59dc12b5b7e8 100644
> --- a/arch/riscv/include/asm/pgalloc.h
> +++ b/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;
> }
> --
> 2.37.2
>
