linux-kernel - [PATCH v2 2/8] crypto: ccp: Detect and reject "invalid" addresses destined for PSP

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Date:   Tue,  6 Apr 2021 15:49:46 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        John Allen <john.allen@....com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...e.de>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Subject: [PATCH v2 2/8] crypto: ccp: Detect and reject "invalid" addresses
 destined for PSP

Explicitly reject using pointers that are not virt_to_phys() friendly
as the source for SEV commands that are sent to the PSP.  The PSP works
with physical addresses, and __pa()/virt_to_phys() will not return the
correct address in these cases, e.g. for a vmalloc'd pointer.  At best,
the bogus address will cause the command to fail, and at worst lead to
system instability.

While it's unlikely that callers will deliberately use a bad pointer for
SEV buffers, a caller can easily use a vmalloc'd pointer unknowingly when
running with CONFIG_VMAP_STACK=y as it's not obvious that putting the
command buffers on the stack would be bad.  The command buffers are
relative  small and easily fit on the stack, and the APIs to do not
document that the incoming pointer must be a physically contiguous,
__pa() friendly pointer.

Cc: Brijesh Singh <brijesh.singh@....com>
Cc: Borislav Petkov <bp@...e.de>
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>
Fixes: 200664d5237f ("crypto: ccp: Add Secure Encrypted Virtualization (SEV) command support")
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 drivers/crypto/ccp/sev-dev.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index ba240d33d26e..3e0d1d6922ba 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -150,6 +150,9 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)

 	sev = psp->sev_data;

+	if (data && WARN_ON_ONCE(!virt_addr_valid(data)))
+		return -EINVAL;
+
 	/* Get the physical address of the command buffer */
 	phys_lsb = data ? lower_32_bits(__psp_pa(data)) : 0;
 	phys_msb = data ? upper_32_bits(__psp_pa(data)) : 0;
-- 
2.31.0.208.g409f899ff0-goog