linux-kernel - [PATCH 2/5] crypto: ccp: Reject SEV commands with mismatching command buffer

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Date:   Fri,  2 Apr 2021 16:36:59 -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>
Subject: [PATCH 2/5] crypto: ccp: Reject SEV commands with mismatching command buffer

WARN on and reject SEV commands that provide a valid data pointer, but do
not have a known, non-zero length.  And conversely, reject commands that
take a command buffer but none is provided.

Aside from sanity checking intput, disallowing a non-null pointer without
a non-zero size will allow a future patch to cleanly handle vmalloc'd
data by copying the data to an internal __pa() friendly buffer.

Note, this also effectively prevents callers from using commands that
have a non-zero length and are not known to the kernel.  This is not an
explicit goal, but arguably the side effect is a good thing from the
kernel's perspective.

Cc: Brijesh Singh <brijesh.singh@....com>
Cc: Borislav Petkov <bp@...e.de>
Cc: Tom Lendacky <thomas.lendacky@....com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 drivers/crypto/ccp/sev-dev.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 6556d220713b..4c513318f16a 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -141,6 +141,7 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
 	struct sev_device *sev;
 	unsigned int phys_lsb, phys_msb;
 	unsigned int reg, ret = 0;
+	int buf_len;
 
 	if (!psp || !psp->sev_data)
 		return -ENODEV;
@@ -150,7 +151,11 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
 
 	sev = psp->sev_data;
 
-	if (data && WARN_ON_ONCE(is_vmalloc_addr(data)))
+	buf_len = sev_cmd_buffer_len(cmd);
+	if (WARN_ON_ONCE(!!data != !!buf_len))
+		return -EINVAL;
+
+	if (WARN_ON_ONCE(data && is_vmalloc_addr(data)))
 		return -EINVAL;
 
 	/* Get the physical address of the command buffer */
@@ -161,7 +166,7 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
 		cmd, phys_msb, phys_lsb, psp_timeout);
 
 	print_hex_dump_debug("(in):  ", DUMP_PREFIX_OFFSET, 16, 2, data,
-			     sev_cmd_buffer_len(cmd), false);
+			     buf_len, false);
 
 	iowrite32(phys_lsb, sev->io_regs + sev->vdata->cmdbuff_addr_lo_reg);
 	iowrite32(phys_msb, sev->io_regs + sev->vdata->cmdbuff_addr_hi_reg);
@@ -197,7 +202,7 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
 	}
 
 	print_hex_dump_debug("(out): ", DUMP_PREFIX_OFFSET, 16, 2, data,
-			     sev_cmd_buffer_len(cmd), false);
+			     buf_len, false);
 
 	return ret;
 }
-- 
2.31.0.208.g409f899ff0-goog