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authorArd Biesheuvel <ardb@kernel.org>2024-02-27 16:19:14 +0100
committerBorislav Petkov (AMD) <bp@alien8.de>2024-03-04 18:12:28 +0100
commitcd0d9d92c8bb46e77de62efd7df13069ddd61e7d (patch)
tree35194564c9b44bc5f42c38ac593ca739064d445b /arch/x86/boot
parent7205f06e847422b66c1506eee01b9998ffc75d76 (diff)
x86/boot: Move mem_encrypt= parsing to the decompressor
The early SME/SEV code parses the command line very early, in order to decide whether or not memory encryption should be enabled, which needs to occur even before the initial page tables are created. This is problematic for a number of reasons: - this early code runs from the 1:1 mapping provided by the decompressor or firmware, which uses a different translation than the one assumed by the linker, and so the code needs to be built in a special way; - parsing external input while the entire kernel image is still mapped writable is a bad idea in general, and really does not belong in security minded code; - the current code ignores the built-in command line entirely (although this appears to be the case for the entire decompressor) Given that the decompressor/EFI stub is an intrinsic part of the x86 bootable kernel image, move the command line parsing there and out of the core kernel. This removes the need to build lib/cmdline.o in a special way, or to use RIP-relative LEA instructions in inline asm blocks. This involves a new xloadflag in the setup header to indicate that mem_encrypt=on appeared on the kernel command line. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de> Tested-by: Tom Lendacky <thomas.lendacky@amd.com> Link: https://lore.kernel.org/r/20240227151907.387873-17-ardb+git@google.com
Diffstat (limited to 'arch/x86/boot')
-rw-r--r--arch/x86/boot/compressed/misc.c15
1 files changed, 15 insertions, 0 deletions
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index bd6857a9f15a..408507e305be 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -372,6 +372,19 @@ unsigned long decompress_kernel(unsigned char *outbuf, unsigned long virt_addr,
}
/*
+ * Set the memory encryption xloadflag based on the mem_encrypt= command line
+ * parameter, if provided.
+ */
+static void parse_mem_encrypt(struct setup_header *hdr)
+{
+ int on = cmdline_find_option_bool("mem_encrypt=on");
+ int off = cmdline_find_option_bool("mem_encrypt=off");
+
+ if (on > off)
+ hdr->xloadflags |= XLF_MEM_ENCRYPTION;
+}
+
+/*
* The compressed kernel image (ZO), has been moved so that its position
* is against the end of the buffer used to hold the uncompressed kernel
* image (VO) and the execution environment (.bss, .brk), which makes sure
@@ -401,6 +414,8 @@ asmlinkage __visible void *extract_kernel(void *rmode, unsigned char *output)
/* Clear flags intended for solely in-kernel use. */
boot_params_ptr->hdr.loadflags &= ~KASLR_FLAG;
+ parse_mem_encrypt(&boot_params_ptr->hdr);
+
sanitize_boot_params(boot_params_ptr);
if (boot_params_ptr->screen_info.orig_video_mode == 7) {