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

Tom Lendacky
2021-04-05T16:26:13Z

On 4/2/21 6:36 PM, Sean Christopherson wrote:
> 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

s/intput/input/

> 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))

Seems a bit confusing to me. Can this just be:

if (WARN_ON_ONCE(data && !buf_len))

Or is this also trying to catch the case where buf_len is non-zero but
data is NULL?

Thanks,
Tom

> + 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;
> }
>