From: "Daniel P. Berrangé" <berrange@redhat.com>
To: Dov Murik <dovmurik@linux.ibm.com>
Cc: "Tom Lendacky" <thomas.lendacky@amd.com>,
"Ashish Kalra" <ashish.kalra@amd.com>,
"Brijesh Singh" <brijesh.singh@amd.com>,
"Eduardo Habkost" <ehabkost@redhat.com>,
"James Bottomley" <jejb@linux.ibm.com>,
"Marcelo Tosatti" <mtosatti@redhat.com>,
qemu-devel@nongnu.org,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
"Tobin Feldman-Fitzthum" <tobin@linux.ibm.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Philippe Mathieu-Daudé" <philmd@redhat.com>
Subject: Re: [PATCH 2/3] sev/i386: Warn if using -kernel with invalid OVMF hashes table area
Date: Wed, 3 Nov 2021 16:07:45 +0000 [thread overview]
Message-ID: <YYKz0QX3AIf9oxYH@redhat.com> (raw)
In-Reply-To: <20211101102136.1706421-3-dovmurik@linux.ibm.com>
On Mon, Nov 01, 2021 at 10:21:35AM +0000, Dov Murik wrote:
> Commit cff03145ed3c ("sev/i386: Introduce sev_add_kernel_loader_hashes
> for measured linux boot", 2021-09-30) introduced measured direct boot
> with -kernel, using an OVMF-designated hashes table which QEMU fills.
>
> However, no checks are performed on the validity of the hashes area
> designated by OVMF. Specifically, if OVMF publishes the
> SEV_HASH_TABLE_RV_GUID entry but it is filled with zeroes, this will
> cause QEMU to write the hashes entries over the first page of the
> guest's memory (GPA 0).
>
> Add validity checks to the published area. If the hashes table area's
> base address is zero, or its size is too small to fit the aligned hashes
> table, warn and skip the hashes entries addition. In such case, the
> following warning will be displayed:
>
> qemu-system-x86_64: warning: SEV: OVMF's hashes table area is invalid (base=0x0 size=0x0)
>
> Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
> Reported-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> target/i386/sev.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index 682b8ccf6c..a20ddb545e 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -1201,13 +1201,18 @@ bool sev_add_kernel_loader_hashes(SevKernelLoaderContext *ctx, Error **errp)
> uint8_t kernel_hash[HASH_SIZE];
> uint8_t *hashp;
> size_t hash_len = HASH_SIZE;
> - int aligned_len;
> + int aligned_len = ROUND_UP(sizeof(SevHashTable), 16);
>
> if (!pc_system_ovmf_table_find(SEV_HASH_TABLE_RV_GUID, &data, NULL)) {
> warn_report("SEV: kernel specified but OVMF has no hash table guid");
> return false;
> }
> area = (SevHashTableDescriptor *)data;
> + if (!area->base || area->size < aligned_len) {
> + warn_report("SEV: OVMF's hashes table area is invalid (base=0x%x size=0x%x)",
> + area->base, area->size);
> + return false;
> + }
I think warn_report is likely a bad idea.
If someone's use case is relying on the hashs being populated, then
we need to be able to error_report and exit, not carry on with a
known broken setup.
Regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
next prev parent reply other threads:[~2021-11-03 16:09 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-01 10:21 [PATCH 0/3] SEV: fixes for -kernel launch with incompatible OVMF Dov Murik
2021-11-01 10:21 ` [PATCH 1/3] sev/i386: Allow launching with -kernel if no OVMF hashes table found Dov Murik
2021-11-01 14:25 ` Tom Lendacky
2021-11-01 17:56 ` Dov Murik
2021-11-03 16:02 ` Daniel P. Berrangé
2021-11-04 18:18 ` Dr. David Alan Gilbert
2021-11-04 18:22 ` Daniel P. Berrangé
2021-11-05 7:41 ` Dov Murik
2021-11-01 10:21 ` [PATCH 2/3] sev/i386: Warn if using -kernel with invalid OVMF hashes table area Dov Murik
2021-11-02 12:36 ` Dr. David Alan Gilbert
2021-11-02 12:56 ` Dov Murik
2021-11-02 18:38 ` Dr. David Alan Gilbert
2021-11-02 19:00 ` Philippe Mathieu-Daudé
2021-11-03 16:07 ` Daniel P. Berrangé [this message]
2021-11-05 7:52 ` Dov Murik
2021-11-01 10:21 ` [PATCH 3/3] sev/i386: Perform padding calculations at compile-time Dov Murik
2021-11-02 11:36 ` Dr. David Alan Gilbert
2021-11-02 11:50 ` Dov Murik
2021-11-03 14:49 ` Philippe Mathieu-Daudé
2021-11-02 10:52 ` [PATCH 0/3] SEV: fixes for -kernel launch with incompatible OVMF Brijesh Singh
2021-11-02 13:22 ` Dov Murik
2021-11-02 14:48 ` Brijesh Singh
2021-11-03 14:08 ` Dr. David Alan Gilbert
2021-11-03 15:44 ` Brijesh Singh
2021-11-05 7:38 ` Dov Murik
2021-11-05 18:32 ` Dov Murik
2021-11-08 21:22 ` Brijesh Singh
2021-11-09 7:34 ` Dov Murik
2021-11-03 16:10 ` Daniel P. Berrangé
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YYKz0QX3AIf9oxYH@redhat.com \
--to=berrange@redhat.com \
--cc=ashish.kalra@amd.com \
--cc=brijesh.singh@amd.com \
--cc=dgilbert@redhat.com \
--cc=dovmurik@linux.ibm.com \
--cc=ehabkost@redhat.com \
--cc=jejb@linux.ibm.com \
--cc=mtosatti@redhat.com \
--cc=pbonzini@redhat.com \
--cc=philmd@redhat.com \
--cc=qemu-devel@nongnu.org \
--cc=thomas.lendacky@amd.com \
--cc=tobin@linux.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).