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 (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@amd.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210406224952.4177376-4-seanjc@google.com>
Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index f53086c..fb08783 100644 (file)
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -142,6 +142,7 @@ 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;
@@ -151,6 +152,10 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
 
        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;
 
@@ -162,7 +167,7 @@ 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);
@@ -198,7 +203,7 @@ 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;
 }