KVM_SEV_SEND_UPDATE_DATA and KVM_SEV_RECEIVE_UPDATE_DATA have an integer
overflow issue. Params.guest_len and offset are both 32bite wide, with a
large params.guest_len the check to confirm a page boundary is not
crossed can falsely pass:
/* Check if we are crossing the page boundary *
offset = params.guest_uaddr & (PAGE_SIZE - 1);
if ((params.guest_len + offset > PAGE_SIZE))
Add an additional check to this conditional to confirm that
params.guest_len itself is not greater than PAGE_SIZE.
The current code is can only overflow with a params.guest_len of greater
than 0xfffff000. And the FW spec says these commands fail with lengths
greater than 16KB. So this issue should not be a security concern
Fixes: 15fb7de1a7f5 ("KVM: SVM: Add KVM_SEV_RECEIVE_UPDATE_DATA command")
Fixes: d3d1af85e2c7 ("KVM: SVM: Add KVM_SEND_UPDATE_DATA command")
Reported-by: Andy Nguyen <[email protected]>
Suggested-by: Thomas Lendacky <[email protected]>
Signed-off-by: Peter Gonda <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Sean Christopherson <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
---
V2
* Updated conditional based on feedback from Tom.
---
arch/x86/kvm/svm/sev.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 273cba809328..3d74facaead8 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1294,7 +1294,7 @@ static int sev_send_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp)
/* Check if we are crossing the page boundary */
offset = params.guest_uaddr & (PAGE_SIZE - 1);
- if ((params.guest_len + offset > PAGE_SIZE))
+ if (params.guest_len > PAGE_SIZE || (params.guest_len + offset) > PAGE_SIZE)
return -EINVAL;
/* Pin guest memory */
@@ -1474,7 +1474,7 @@ static int sev_receive_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp)
/* Check if we are crossing the page boundary */
offset = params.guest_uaddr & (PAGE_SIZE - 1);
- if ((params.guest_len + offset > PAGE_SIZE))
+ if (params.guest_len > PAGE_SIZE || (params.guest_len + offset) > PAGE_SIZE)
return -EINVAL;
hdr = psp_copy_user_blob(params.hdr_uaddr, params.hdr_len);
--
2.39.1.519.gcb327c4b5f-goog
On 2/7/23 11:13, Peter Gonda wrote:
> KVM_SEV_SEND_UPDATE_DATA and KVM_SEV_RECEIVE_UPDATE_DATA have an integer
> overflow issue. Params.guest_len and offset are both 32bite wide, with a
> large params.guest_len the check to confirm a page boundary is not
> crossed can falsely pass:
>
> /* Check if we are crossing the page boundary *
> offset = params.guest_uaddr & (PAGE_SIZE - 1);
> if ((params.guest_len + offset > PAGE_SIZE))
>
> Add an additional check to this conditional to confirm that
> params.guest_len itself is not greater than PAGE_SIZE.
>
> The current code is can only overflow with a params.guest_len of greater
> than 0xfffff000. And the FW spec says these commands fail with lengths
> greater than 16KB. So this issue should not be a security concern
>
> Fixes: 15fb7de1a7f5 ("KVM: SVM: Add KVM_SEV_RECEIVE_UPDATE_DATA command")
> Fixes: d3d1af85e2c7 ("KVM: SVM: Add KVM_SEND_UPDATE_DATA command")
> Reported-by: Andy Nguyen <[email protected]>
> Suggested-by: Thomas Lendacky <[email protected]>
> Signed-off-by: Peter Gonda <[email protected]>
> Cc: David Rientjes <[email protected]>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Sean Christopherson <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
Reviewed-by: Tom Lendacky <[email protected]>
> ---
>
> V2
> * Updated conditional based on feedback from Tom.
>
> ---
> arch/x86/kvm/svm/sev.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 273cba809328..3d74facaead8 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1294,7 +1294,7 @@ static int sev_send_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp)
>
> /* Check if we are crossing the page boundary */
> offset = params.guest_uaddr & (PAGE_SIZE - 1);
> - if ((params.guest_len + offset > PAGE_SIZE))
> + if (params.guest_len > PAGE_SIZE || (params.guest_len + offset) > PAGE_SIZE)
> return -EINVAL;
>
> /* Pin guest memory */
> @@ -1474,7 +1474,7 @@ static int sev_receive_update_data(struct kvm *kvm, struct kvm_sev_cmd *argp)
>
> /* Check if we are crossing the page boundary */
> offset = params.guest_uaddr & (PAGE_SIZE - 1);
> - if ((params.guest_len + offset > PAGE_SIZE))
> + if (params.guest_len > PAGE_SIZE || (params.guest_len + offset) > PAGE_SIZE)
> return -EINVAL;
>
> hdr = psp_copy_user_blob(params.hdr_uaddr, params.hdr_len);
For now at least, I want to keep with "KVM: SVM:" instead of using "KVM: SEV:".
Many commits that touch SEV aren't strictly isolated to SEV, which means the "SEV"
tag is unreliable. There's also the question of taggin SEV vs. SEV-ES vs. SEV-SNP.
It's usually easy enough to squeeze SEV (or SEV-ES or SNP) into the shortlog, e.g.
KVM: SVM: Fix potential overflow in SEV's send|receive_update_data()
On Tue, Feb 07, 2023, Peter Gonda wrote:
> KVM_SEV_SEND_UPDATE_DATA and KVM_SEV_RECEIVE_UPDATE_DATA have an integer
> overflow issue. Params.guest_len and offset are both 32bite wide, with a
"32 bits"
> large params.guest_len the check to confirm a page boundary is not
> crossed can falsely pass:
>
> /* Check if we are crossing the page boundary *
> offset = params.guest_uaddr & (PAGE_SIZE - 1);
> if ((params.guest_len + offset > PAGE_SIZE))
>
> Add an additional check to this conditional to confirm that
Eh, "to this conditional" is unnecessarily precise.
> params.guest_len itself is not greater than PAGE_SIZE.
>
> The current code is can only overflow with a params.guest_len of greater
"is can", though I vote to omit the "current code" part entirely, it should be
obvious that this is talking about the pre-patched code.
> than 0xfffff000. And the FW spec says these commands fail with lengths
> greater than 16KB. So this issue should not be a security concern
Slightly reworded, how about this for the "not a security concern" disclaimer?
Note, this isn't a security concern as overflow can happen if and only if
params.guest_len is greater than 0xfffff000, and the FW spec says these
commands fail with lengths greater than 16KB, i.e. the PSP will detect
KVM's goof.
No need to send a v3, I'll fix up the changelog when applying. Holler if you
disagree with anything though.
Thanks!
On Tue, 07 Feb 2023 09:13:54 -0800, Peter Gonda wrote:
> KVM_SEV_SEND_UPDATE_DATA and KVM_SEV_RECEIVE_UPDATE_DATA have an integer
> overflow issue. Params.guest_len and offset are both 32bite wide, with a
> large params.guest_len the check to confirm a page boundary is not
> crossed can falsely pass:
>
> /* Check if we are crossing the page boundary *
> offset = params.guest_uaddr & (PAGE_SIZE - 1);
> if ((params.guest_len + offset > PAGE_SIZE))
>
> [...]
Applied to kvm-x86 svm, thanks!
[1/1] KVM: sev: Fix potential overflow send|recieve_update_data
https://github.com/kvm-x86/linux/commit/f94f053aa3a5
--
https://github.com/kvm-x86/linux/tree/next
https://github.com/kvm-x86/linux/tree/fixes