[RFC,01/17] x86/boot: Check boot param's cc_blob_address for direct boot mode
Commit Message
From: Tianyu Lan <tiala@microsoft.com>
Hypervisor may pass cc blob address directly into boot param's cc
blob address in the direct boot mode. Check cc blcb hdr magic first
in the sev_enable() and use it as cc blob address if check successfully.
Signed-off-by: Tianyu Lan <tiala@microsoft.com>
---
arch/x86/boot/compressed/sev.c | 27 ++++++++++++++++++++-------
1 file changed, 20 insertions(+), 7 deletions(-)
Comments
On Wed, Nov 09, 2022 at 03:53:36PM -0500, Tianyu Lan wrote:
> From: Tianyu Lan <tiala@microsoft.com>
>
> Hypervisor may pass cc blob address directly into boot param's cc
> blob address in the direct boot mode. Check cc blcb hdr magic first
> in the sev_enable() and use it as cc blob address if check successfully.
>
> Signed-off-by: Tianyu Lan <tiala@microsoft.com>
> ---
> arch/x86/boot/compressed/sev.c | 27 ++++++++++++++++++++-------
> 1 file changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> index c93930d5ccbd..960968f8bf75 100644
> --- a/arch/x86/boot/compressed/sev.c
> +++ b/arch/x86/boot/compressed/sev.c
> @@ -272,17 +272,24 @@ static void enforce_vmpl0(void)
>
> void sev_enable(struct boot_params *bp)
> {
> + struct cc_blob_sev_info *cc_info;
> unsigned int eax, ebx, ecx, edx;
> 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.
> + * bp->cc_blob_address should only be set by boot/compressed
> + * kernel and hypervisor with direct boot mode. Initialize it
> + * to 0 after checking in order to ensure that uninitialized
> + * values from buggy bootloaders aren't propagated.
> */
> - if (bp)
> - bp->cc_blob_address = 0;
> + if (bp) {
> + cc_info = (struct cc_blob_sev_info *)(unsigned long)
> + bp->cc_blob_address;
> +
> + if (cc_info->magic != CC_BLOB_SEV_HDR_MAGIC)
> + bp->cc_blob_address = 0;
It doesn't seem great to rely on SEV_HDR_MAGIC to determine whether
bp->cc_blob_address is valid or not since it is only a 32-bit value.
Would it be possible to use a setup_data entry of type SETUP_CC_BLOB
in bp->hdr.setup_data instead? There's already handling for that in
find_cc_blob_setup_data() so it should "just work".
-Mike
On 11/10/2022 7:39 AM, Michael Roth wrote:
>> - * 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.
>> + * bp->cc_blob_address should only be set by boot/compressed
>> + * kernel and hypervisor with direct boot mode. Initialize it
>> + * to 0 after checking in order to ensure that uninitialized
>> + * values from buggy bootloaders aren't propagated.
>> */
>> - if (bp)
>> - bp->cc_blob_address = 0;
>> + if (bp) {
>> + cc_info = (struct cc_blob_sev_info *)(unsigned long)
>> + bp->cc_blob_address;
>> +
>> + if (cc_info->magic != CC_BLOB_SEV_HDR_MAGIC)
>> + bp->cc_blob_address = 0;
> It doesn't seem great to rely on SEV_HDR_MAGIC to determine whether
> bp->cc_blob_address is valid or not since it is only a 32-bit value.
>
> Would it be possible to use a setup_data entry of type SETUP_CC_BLOB
> in bp->hdr.setup_data instead? There's already handling for that in
> find_cc_blob_setup_data() so it should "just work".
Hi Michael:
Thanks for your review. I will have a try. Hypervisor may set
cc_blob_address directly and so propose this.
@@ -272,17 +272,24 @@ static void enforce_vmpl0(void)
void sev_enable(struct boot_params *bp)
{
+ struct cc_blob_sev_info *cc_info;
unsigned int eax, ebx, ecx, edx;
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.
+ * bp->cc_blob_address should only be set by boot/compressed
+ * kernel and hypervisor with direct boot mode. Initialize it
+ * to 0 after checking in order to ensure that uninitialized
+ * values from buggy bootloaders aren't propagated.
*/
- if (bp)
- bp->cc_blob_address = 0;
+ if (bp) {
+ cc_info = (struct cc_blob_sev_info *)(unsigned long)
+ bp->cc_blob_address;
+
+ if (cc_info->magic != CC_BLOB_SEV_HDR_MAGIC)
+ bp->cc_blob_address = 0;
+ }
/*
* Setup/preliminary detection of SNP. This will be sanity-checked
@@ -374,6 +381,10 @@ static struct cc_blob_sev_info *find_cc_blob(struct boot_params *bp)
{
struct cc_blob_sev_info *cc_info;
+ /* Boot kernel would have passed the CC blob via boot_params. */
+ if (bp->cc_blob_address)
+ return (struct cc_blob_sev_info *)(unsigned long)bp->cc_blob_address;
+
cc_info = find_cc_blob_efi(bp);
if (cc_info)
goto found_cc_info;
@@ -416,9 +427,11 @@ bool snp_init(struct boot_params *bp)
/*
* Pass run-time kernel a pointer to CC info via boot_params so EFI
* config table doesn't need to be searched again during early startup
- * phase.
+ * phase. Hypervisor also may popualte cc_blob_address directyly
+ * in direct boot mode.
*/
- bp->cc_blob_address = (u32)(unsigned long)cc_info;
+ if (!bp->cc_blob_address)
+ bp->cc_blob_address = (u32)(unsigned long)cc_info;
return true;
}