KVM: sev: Fix potential overflow send|recieve_update_data
Subsystems (4)
PATCH v2 1/1 KVM: sev: Fix potential overflow send|recieve_update_data
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
---
V2
* Updated conditional based on feedback from Tom.
--- arch/x86/kvm/svm/sev.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
arch/x86/kvm/svm/sev.c +2 -2
@@ -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);
Signature · 1 line
2.39.1.519.gcb327c4b5f-goog
Quoted 16 lines · Peter Gonda
KVM_SEV_SEND_UPDATE_DATAandKVM_SEV_RECEIVE_UPDATE_DATAhave 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
Quoted 11 lines
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]>
Quoted 31 lines
---
V2
* Updated conditional based on feedback from Tom.--- arch/x86/kvm/svm/sev.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)arch/x86/kvm/svm/sev.c +2
-2@@ -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);
Sean Christopherson
maintainerFor 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()
Quoted 2 lines · Peter Gonda
KVM_SEV_SEND_UPDATE_DATAandKVM_SEV_RECEIVE_UPDATE_DATAhave an integer overflow issue. Params.guest_len and offset are both 32bite wide, with a
"32 bits"
Quoted 8 lines
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.
Quoted 3 lines
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.
Quoted 2 lines
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!
Quoted 10 lines · Peter Gonda
KVM_SEV_SEND_UPDATE_DATAandKVM_SEV_RECEIVE_UPDATE_DATAhave 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
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https://github.com/kvm-x86/linux/tree/next
https://github.com/kvm-x86/linux/tree/fixes