Messages in this thread | | | Date | Tue, 16 Apr 2024 11:17:38 -0500 | Subject | Re: [PATCH v3 10/14] configfs-tsm: Allow the privlevel_floor attribute to be updated | From | Tom Lendacky <> |
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On 4/16/24 10:57, Dan Williams wrote: > Tom Lendacky wrote: >> On 4/15/24 23:55, Dan Williams wrote: >>> Tom Lendacky wrote: >>>> With the introduction of an SVSM, Linux will be running at a non-zero >>>> VMPL. Any request for an attestation report at a higher priviledge VMPL >>>> than what Linux is currently running will result in an error. Allow for >>>> the privlevel_floor attribute to be updated dynamically so that the >>>> attribute may be set dynamically. >>>> >>>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com> >>>> --- >>>> drivers/virt/coco/sev-guest/sev-guest.c | 5 ++++- >>>> include/linux/tsm.h | 2 +- >>>> 2 files changed, 5 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c >>>> index 1ff897913bf4..bba6531cb606 100644 >>>> --- a/drivers/virt/coco/sev-guest/sev-guest.c >>>> +++ b/drivers/virt/coco/sev-guest/sev-guest.c >>>> @@ -885,7 +885,7 @@ static int sev_report_new(struct tsm_report *report, void *data) >>>> return 0; >>>> } >>>> >>>> -static const struct tsm_ops sev_tsm_ops = { >>>> +static struct tsm_ops sev_tsm_ops = { >>>> .name = KBUILD_MODNAME, >>>> .report_new = sev_report_new, >>>> }; >>>> @@ -972,6 +972,9 @@ static int __init sev_guest_probe(struct platform_device *pdev) >>>> snp_dev->input.resp_gpa = __pa(snp_dev->response); >>>> snp_dev->input.data_gpa = __pa(snp_dev->certs_data); >>>> >>>> + /* Set the privlevel_floor attribute based on the current VMPL */ >>>> + sev_tsm_ops.privlevel_floor = snp_get_vmpl(); >>> >>> Why is this not vmpck_id? >> >> Good catch, this probably should be pulled out separately and submitted >> as a Fixes: against the current support. If you think it's important >> enough, I can do that and put this at the beginning of the series. Or I >> can just modify this to use the vmpck_id value. Any preference? > > I dunno, you tell me. What breaks if privlevel_floor is mismatched vs > vmpl and/or vmpck_id? If it warrants a "Fixes:" it should probably be > broken out. > > However, I *guess* it is just adding some sanity checking precision to > userspace requests and makes some input validation not catch errors when > userspace tries to generate reports from the wrong level, right? I.e. > privlevel_floor may be lower than expected, but userspace should not be > depending on that since the report generation will fail.
Yeah, it just results in a different type of error. If the VMPL specified by the user is numerically lower than the vmpck_id, then the request will fail with a specific return code value. With the change to privlevel_floor to use vmpck_id, then you would just get the error that much sooner when trying to set a value that is lower than the floor.
Since I don't think the vmpck_id module parameter is a common case today, let's just leave that change in this patch.
Thanks, Tom
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