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    SubjectRe: [PATCHv10 05/11] x86/boot/compressed: Handle unaccepted memory
    On Mon, 8 May 2023 at 01:46, Kirill A. Shutemov
    <kirill.shutemov@linux.intel.com> wrote:
    >
    > The firmware will pre-accept the memory used to run the stub. But, the
    > stub is responsible for accepting the memory into which it decompresses
    > the main kernel. Accept memory just before decompression starts.
    >
    > The stub is also responsible for choosing a physical address in which to
    > place the decompressed kernel image. The KASLR mechanism will randomize
    > this physical address. Since the unaccepted memory region is relatively
    > small, KASLR would be quite ineffective if it only used the pre-accepted
    > area (EFI_CONVENTIONAL_MEMORY). Ensure that KASLR randomizes among the
    > entire physical address space by also including EFI_UNACCEPTED_MEMORY.
    >
    > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

    Acked-by: Ard Biesheuvel <ardb@kernel.org>

    > ---
    > arch/x86/boot/compressed/Makefile | 2 +-
    > arch/x86/boot/compressed/efi.h | 1 +
    > arch/x86/boot/compressed/kaslr.c | 35 ++++++++++++++++--------
    > arch/x86/boot/compressed/mem.c | 18 ++++++++++++
    > arch/x86/boot/compressed/misc.c | 6 ++++
    > arch/x86/boot/compressed/misc.h | 6 ++++
    > arch/x86/include/asm/unaccepted_memory.h | 2 ++
    > 7 files changed, 57 insertions(+), 13 deletions(-)
    >
    > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
    > index f62c02348f9a..74f7adee46ad 100644
    > --- a/arch/x86/boot/compressed/Makefile
    > +++ b/arch/x86/boot/compressed/Makefile
    > @@ -107,7 +107,7 @@ endif
    >
    > vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
    > vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o $(obj)/tdcall.o
    > -vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/bitmap.o $(obj)/mem.o
    > +vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/bitmap.o $(obj)/find.o $(obj)/mem.o
    >
    > vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
    > vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_mixed.o
    > diff --git a/arch/x86/boot/compressed/efi.h b/arch/x86/boot/compressed/efi.h
    > index 7db2f41b54cd..cf475243b6d5 100644
    > --- a/arch/x86/boot/compressed/efi.h
    > +++ b/arch/x86/boot/compressed/efi.h
    > @@ -32,6 +32,7 @@ typedef struct {
    > } efi_table_hdr_t;
    >
    > #define EFI_CONVENTIONAL_MEMORY 7
    > +#define EFI_UNACCEPTED_MEMORY 15
    >
    > #define EFI_MEMORY_MORE_RELIABLE \
    > ((u64)0x0000000000010000ULL) /* higher reliability */
    > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
    > index 454757fbdfe5..749f0fe7e446 100644
    > --- a/arch/x86/boot/compressed/kaslr.c
    > +++ b/arch/x86/boot/compressed/kaslr.c
    > @@ -672,6 +672,28 @@ static bool process_mem_region(struct mem_vector *region,
    > }
    >
    > #ifdef CONFIG_EFI
    > +
    > +/*
    > + * Only EFI_CONVENTIONAL_MEMORY and EFI_UNACCEPTED_MEMORY (if supported) are
    > + * guaranteed to be free.
    > + *
    > + * It is more conservative in picking free memory than the EFI spec allows:
    > + *
    > + * According to the spec, EFI_BOOT_SERVICES_{CODE|DATA} are also free memory
    > + * and thus available to place the kernel image into, but in practice there's
    > + * firmware where using that memory leads to crashes.
    > + */
    > +static inline bool memory_type_is_free(efi_memory_desc_t *md)
    > +{
    > + if (md->type == EFI_CONVENTIONAL_MEMORY)
    > + return true;
    > +
    > + if (md->type == EFI_UNACCEPTED_MEMORY)
    > + return IS_ENABLED(CONFIG_UNACCEPTED_MEMORY);
    > +
    > + return false;
    > +}
    > +
    > /*
    > * Returns true if we processed the EFI memmap, which we prefer over the E820
    > * table if it is available.
    > @@ -716,18 +738,7 @@ process_efi_entries(unsigned long minimum, unsigned long image_size)
    > for (i = 0; i < nr_desc; i++) {
    > md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
    >
    > - /*
    > - * Here we are more conservative in picking free memory than
    > - * the EFI spec allows:
    > - *
    > - * According to the spec, EFI_BOOT_SERVICES_{CODE|DATA} are also
    > - * free memory and thus available to place the kernel image into,
    > - * but in practice there's firmware where using that memory leads
    > - * to crashes.
    > - *
    > - * Only EFI_CONVENTIONAL_MEMORY is guaranteed to be free.
    > - */
    > - if (md->type != EFI_CONVENTIONAL_MEMORY)
    > + if (!memory_type_is_free(md))
    > continue;
    >
    > if (efi_soft_reserve_enabled() &&
    > diff --git a/arch/x86/boot/compressed/mem.c b/arch/x86/boot/compressed/mem.c
    > index 6b15a0ed8b54..de858a5180b6 100644
    > --- a/arch/x86/boot/compressed/mem.c
    > +++ b/arch/x86/boot/compressed/mem.c
    > @@ -3,12 +3,15 @@
    > #include "../cpuflags.h"
    > #include "bitmap.h"
    > #include "error.h"
    > +#include "find.h"
    > #include "math.h"
    >
    > #define PMD_SHIFT 21
    > #define PMD_SIZE (_AC(1, UL) << PMD_SHIFT)
    > #define PMD_MASK (~(PMD_SIZE - 1))
    >
    > +extern struct boot_params *boot_params;
    > +
    > static inline void __accept_memory(phys_addr_t start, phys_addr_t end)
    > {
    > /* Platform-specific memory-acceptance call goes here */
    > @@ -71,3 +74,18 @@ void process_unaccepted_memory(struct boot_params *params, u64 start, u64 end)
    > bitmap_set((unsigned long *)params->unaccepted_memory,
    > start / PMD_SIZE, (end - start) / PMD_SIZE);
    > }
    > +
    > +void accept_memory(phys_addr_t start, phys_addr_t end)
    > +{
    > + unsigned long range_start, range_end;
    > + unsigned long *bitmap, bitmap_size;
    > +
    > + bitmap = (unsigned long *)boot_params->unaccepted_memory;
    > + range_start = start / PMD_SIZE;
    > + bitmap_size = DIV_ROUND_UP(end, PMD_SIZE);
    > +
    > + for_each_set_bitrange_from(range_start, range_end, bitmap, bitmap_size) {
    > + __accept_memory(range_start * PMD_SIZE, range_end * PMD_SIZE);
    > + bitmap_clear(bitmap, range_start, range_end - range_start);
    > + }
    > +}
    > diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
    > index 014ff222bf4b..186bfd53e042 100644
    > --- a/arch/x86/boot/compressed/misc.c
    > +++ b/arch/x86/boot/compressed/misc.c
    > @@ -455,6 +455,12 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
    > #endif
    >
    > debug_putstr("\nDecompressing Linux... ");
    > +
    > + if (boot_params->unaccepted_memory) {
    > + debug_putstr("Accepting memory... ");
    > + accept_memory(__pa(output), __pa(output) + needed_size);
    > + }
    > +
    > __decompress(input_data, input_len, NULL, NULL, output, output_len,
    > NULL, error);
    > entry_offset = parse_elf(output);
    > diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
    > index 2f155a0e3041..9663d1839f54 100644
    > --- a/arch/x86/boot/compressed/misc.h
    > +++ b/arch/x86/boot/compressed/misc.h
    > @@ -247,4 +247,10 @@ static inline unsigned long efi_find_vendor_table(struct boot_params *bp,
    > }
    > #endif /* CONFIG_EFI */
    >
    > +#ifdef CONFIG_UNACCEPTED_MEMORY
    > +void accept_memory(phys_addr_t start, phys_addr_t end);
    > +#else
    > +static inline void accept_memory(phys_addr_t start, phys_addr_t end) {}
    > +#endif
    > +
    > #endif /* BOOT_COMPRESSED_MISC_H */
    > diff --git a/arch/x86/include/asm/unaccepted_memory.h b/arch/x86/include/asm/unaccepted_memory.h
    > index df0736d32858..41fbfc798100 100644
    > --- a/arch/x86/include/asm/unaccepted_memory.h
    > +++ b/arch/x86/include/asm/unaccepted_memory.h
    > @@ -7,4 +7,6 @@ struct boot_params;
    >
    > void process_unaccepted_memory(struct boot_params *params, u64 start, u64 num);
    >
    > +void accept_memory(phys_addr_t start, phys_addr_t end);
    > +
    > #endif
    > --
    > 2.39.3
    >

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