Messages in this thread | | | Date | Wed, 17 May 2023 10:52:34 -0500 | Subject | Re: [PATCHv11 4/9] x86/boot/compressed: Handle unaccepted memory | From | Tom Lendacky <> |
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On 5/13/23 17:04, Kirill A. Shutemov 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>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
> --- > arch/x86/boot/compressed/efi.h | 1 + > arch/x86/boot/compressed/kaslr.c | 35 +++++++++++++++++++++----------- > arch/x86/boot/compressed/misc.c | 6 ++++++ > arch/x86/boot/compressed/misc.h | 6 ++++++ > 4 files changed, 36 insertions(+), 12 deletions(-) > > 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/misc.c b/arch/x86/boot/compressed/misc.c > index 014ff222bf4b..eb8df0d4ad51 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 (IS_ENABLED(CONFIG_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 */
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