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x86/boot: Don't propagate uninitialized boot_params->cc_blob_address

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In some cases, bootloaders will leave boot_params->cc_blob_address
uninitialized rather than zeroing it out. This field is only meant to be
set by the boot/compressed kernel in order to pass information to the
uncompressed kernel when SEV-SNP support is enabled.

Therefore, there are no cases where the bootloader-provided values
should be treated as anything other than garbage. Otherwise, the
uncompressed kernel may attempt to access this bogus address, leading to
a crash during early boot.

Normally, sanitize_boot_params() would be used to clear out such fields
but that happens too late: sev_enable() may have already initialized
it to a valid value that should not be zeroed out. Instead, have
sev_enable() zero it out unconditionally beforehand.

Also ensure this happens for !CONFIG_AMD_MEM_ENCRYPT as well by also
including this handling in the sev_enable() stub function.

  [ bp: Massage commit message and comments. ]

Fixes: b190a043c49a ("x86/sev: Add SEV-SNP feature detection/setup")
Reported-by: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Reported-by: watnuss@gmx.de
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216387
Link: https://lore.kernel.org/r/20220823160734.89036-1-michael.roth@amd.com
This commit is contained in:
Michael Roth 2022-08-23 11:07:34 -05:00 committed by Borislav Petkov
parent ea902bcc19
commit 4b1c742407
2 changed files with 19 additions and 1 deletions
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12
arch/x86/boot/compressed/misc.h
View File

@ -132,7 +132,17 @@ void snp_set_page_private(unsigned long paddr);
void snp_set_page_shared(unsigned long paddr);
void sev_prep_identity_maps(unsigned long top_level_pgt);
#else
static inline void sev_enable(struct boot_params *bp) { }
static inline void sev_enable(struct boot_params *bp)
{
/*
* bp->cc_blob_address should only be set by boot/compressed kernel.
* Initialize it to 0 unconditionally (thus here in this stub too) to
* ensure that uninitialized values from buggy bootloaders aren't
* propagated.
*/
if (bp)
bp->cc_blob_address = 0;
}
static inline void sev_es_shutdown_ghcb(void) { }
static inline bool sev_es_check_ghcb_fault(unsigned long address)
{

8
arch/x86/boot/compressed/sev.c
View File

@ -276,6 +276,14 @@ void sev_enable(struct boot_params *bp)
struct msr m;
bool snp;
/*
* bp->cc_blob_address should only be set by boot/compressed kernel.
* Initialize it to 0 to ensure that uninitialized values from
* buggy bootloaders aren't propagated.
*/
if (bp)
bp->cc_blob_address = 0;
/*
* Setup/preliminary detection of SNP. This will be sanity-checked
* against CPUID/MSR values later.