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

Sean Christopherson
2021-04-02T23:37:29Z

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@amd.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.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