On Tue, 6 Sept 2022 at 12:41, Evgeniy Baskov <baskov@xxxxxxxxx> wrote:
>
> After every implicit mapping is removed, this code is no longer needed.
>
> Remove memory mapping from page fault handler to ensure that there are
> no hidden invalid memory accesses.
>
> Signed-off-by: Evgeniy Baskov <baskov@xxxxxxxxx>
I don't grok this 100% but to me, it seems not having to rely on a
page fault handler to ensure that the 1:1 mapping has sufficient
coverage is a win so
Acked-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> ---
> arch/x86/boot/compressed/ident_map_64.c | 26 ++++++++++---------------
> 1 file changed, 10 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
> index 880e08293023..c20cd31e665f 100644
> --- a/arch/x86/boot/compressed/ident_map_64.c
> +++ b/arch/x86/boot/compressed/ident_map_64.c
> @@ -385,27 +385,21 @@ void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
> {
> unsigned long address = native_read_cr2();
> unsigned long end;
> - bool ghcb_fault;
> + char *msg;
>
> - ghcb_fault = sev_es_check_ghcb_fault(address);
> + if (sev_es_check_ghcb_fault(address))
> + msg = "Page-fault on GHCB page:";
> + else
> + msg = "Unexpected page-fault:";
>
> address &= PMD_MASK;
> end = address + PMD_SIZE;
>
> /*
> - * Check for unexpected error codes. Unexpected are:
> - * - Faults on present pages
> - * - User faults
> - * - Reserved bits set
> - */
> - if (error_code & (X86_PF_PROT | X86_PF_USER | X86_PF_RSVD))
> - do_pf_error("Unexpected page-fault:", error_code, address, regs->ip);
> - else if (ghcb_fault)
> - do_pf_error("Page-fault on GHCB page:", error_code, address, regs->ip);
> -
> - /*
> - * Error code is sane - now identity map the 2M region around
> - * the faulting address.
> + * Since all memory allocations are made explicit
> + * now, every page fault at this stage is an
> + * error and the error handler is there only
> + * for debug purposes.
> */
> - kernel_add_identity_map(address, end, MAP_WRITE);
> + do_pf_error(msg, error_code, address, regs->ip);
> }
> --
> 2.35.1
>
