x86/boot/compressed: Handle unaccepted memory

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 accepted 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>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20230606142637.5171-5-kirill.shutemov@linux.intel.com

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 2f155a0e3041..964fe903a1cd 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -247,4 +247,14 @@ static inline unsigned long efi_find_vendor_table(struct boot_params *bp,
 }
 #endif /* CONFIG_EFI */
 
+#ifdef CONFIG_UNACCEPTED_MEMORY
+bool init_unaccepted_memory(void);
+#else
+static inline bool init_unaccepted_memory(void) { return false; }
+#endif
+
+/* Defined in EFI stub */
+extern struct efi_unaccepted_memory *unaccepted_table;
+void accept_memory(phys_addr_t start, phys_addr_t end);
+
 #endif /* BOOT_COMPRESSED_MISC_H */