[PATCH 5.10 114/120] crypto: ccp: Reject SEV commands with mismatching command buffer

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From: Sean Christopherson <seanjc@xxxxxxxxxx>

commit d5760dee127bf6f390b05e747369d7c37ae1a7b8 upstream.

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 (data is null).

Aside from sanity checking input, 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@xxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20210406224952.4177376-4-seanjc@xxxxxxxxxx>
Reviewed-by: Brijesh Singh <brijesh.singh@xxxxxxx>
Acked-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Ben Hutchings <benh@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/crypto/ccp/sev-dev.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -156,6 +156,7 @@ static int __sev_do_cmd_locked(int cmd,
 	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;
@@ -165,6 +166,10 @@ static int __sev_do_cmd_locked(int cmd,
 
 	sev = psp->sev_data;
 
+	buf_len = sev_cmd_buffer_len(cmd);
+	if (WARN_ON_ONCE(!data != !buf_len))
+		return -EINVAL;
+
 	if (data && WARN_ON_ONCE(!virt_addr_valid(data)))
 		return -EINVAL;
 
@@ -176,7 +181,7 @@ static int __sev_do_cmd_locked(int cmd,
 		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);
@@ -212,7 +217,7 @@ static int __sev_do_cmd_locked(int cmd,
 	}
 
 	print_hex_dump_debug("(out): ", DUMP_PREFIX_OFFSET, 16, 2, data,
-			     sev_cmd_buffer_len(cmd), false);
+			     buf_len, false);
 
 	return ret;
 }





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