Messages in this thread Patch in this message | | | From | Ard Biesheuvel <> | Date | Wed, 8 Mar 2023 11:28:55 +0100 | Subject | Re: [PATCH v4 08/26] x86/boot: Map memory explicitly |
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On Wed, 8 Mar 2023 at 10:38, Ard Biesheuvel <ardb@kernel.org> wrote: > > On Thu, 15 Dec 2022 at 13:38, Evgeniy Baskov <baskov@ispras.ru> wrote: > > > > Implicit mappings hide possible memory errors, e.g. allocations for > > ACPI tables were not included in boot page table size. > > > > Replace all implicit mappings from page fault handler with > > explicit mappings. > > > > I agree with the motivation but this patch seems to break the boot > under SeaBIOS/QEMU, and I imagine other legacy BIOS boot scenarios as > well. > > Naively, I would assume that there is simply a legacy BIOS region that > we fail to map here, but I am fairly clueless when it comes to non-EFI > x86 boot so take this with a grain of salt. >
The below seems to help - not sure why exactly, but apparently legacy BIOS needs the bootparams struct to be mapped writable?
--- a/arch/x86/boot/compressed/kaslr.c +++ b/arch/x86/boot/compressed/kaslr.c @@ -31,6 +31,7 @@ #include <linux/ctype.h> #include <generated/utsversion.h> #include <generated/utsrelease.h> +#include <asm/shared/pgtable.h>
#define _SETUP #include <asm/setup.h> /* For COMMAND_LINE_SIZE */ @@ -688,7 +689,7 @@ process_efi_entries(unsigned long minimum, unsigned long image_size) u32 nr_desc; int i;
- kernel_add_identity_map((unsigned long)e, (unsigned long)(e + 1), 0); + kernel_add_identity_map((unsigned long)e, (unsigned long)(e + 1), MAP_WRITE);
signature = (char *)&e->efi_loader_signature; if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
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