Commit f30470c1 authored by Ashish Kalra's avatar Ashish Kalra Committed by Borislav Petkov (AMD)
Browse files

x86/boot: Skip video memory access in the decompressor for SEV-ES/SNP 



Accessing guest video memory/RAM in the decompressor causes guest
termination as the boot stage2 #VC handler for SEV-ES/SNP systems does
not support MMIO handling.

This issue is observed during a SEV-ES/SNP guest kexec as kexec -c adds
screen_info to the boot parameters passed to the second kernel, which
causes console output to be dumped to both video and serial.

As the decompressor output gets cleared really fast, it is preferable to
get the console output only on serial, hence, skip accessing the video
RAM during decompressor stage to prevent guest termination.

Serial console output during decompressor stage works as boot stage2 #VC
handler already supports handling port I/O.

  [ bp: Massage. ]

Suggested-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Suggested-by: default avatarThomas Lendacky <thomas.lendacky@amd.com>
Signed-off-by: default avatarAshish Kalra <ashish.kalra@amd.com>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: default avatarKuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: default avatarTom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/8a55ea86524c686e575d273311acbe57ce8cee23.1722520012.git.ashish.kalra@amd.com
parent 0a895c0d

arch/x86/boot/compressed/misc.c

+15 −0
Original line number Diff line number Diff line
@@ -385,6 +385,19 @@ static void parse_mem_encrypt(struct setup_header *hdr) 
		hdr->xloadflags |= XLF_MEM_ENCRYPTION;

}



static void early_sev_detect(void)

{

	/*

	 * Accessing video memory causes guest termination because

	 * the boot stage2 #VC handler of SEV-ES/SNP guests does not

	 * support MMIO handling and kexec -c adds screen_info to the

	 * boot parameters passed to the kexec kernel, which causes

	 * console output to be dumped to both video and serial.

	 */

	if (sev_status & MSR_AMD64_SEV_ES_ENABLED)

		lines = cols = 0;

}



/*

 * 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
@@ -440,6 +453,8 @@ asmlinkage __visible void *extract_kernel(void *rmode, unsigned char *output) 
	 */

	early_tdx_detect();



	early_sev_detect();



	console_init();



	/*