linux-kernel - Re: [PATCH] riscv: Sync efi page table's kernel mappings before switching

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Date:   Wed, 23 Nov 2022 11:12:35 -0800
From:   Atish Patra <atishp@...shpatra.org>
To:     Emil Renner Berthing <emil.renner.berthing@...onical.com>
Cc:     Alexandre Ghiti <alexghiti@...osinc.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
        linux-efi@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: Sync efi page table's kernel mappings before switching

On Wed, Nov 23, 2022 at 9:19 AM Emil Renner Berthing
<emil.renner.berthing@...onical.com> wrote:
>
> Hi Alexandre,
>
> On Mon, 21 Nov 2022 at 14:33, Alexandre Ghiti <alexghiti@...osinc.com> 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@...osinc.com>
>
> 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@...onical.com>
>
> > ---
> >  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
> >

Thanks for the fix. With the correct Fixes tag in commit description:A

Reviewed-by: Atish Patra <atishp@...osinc.com>


-- 
Regards,
Atish