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

[Christophe Leroy]

Le 03/04/2021 à 01:36, Sean Christopherson a écrit :

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.si...@amd.com>
Cc: Borislav Petkov <b...@suse.de>
Cc: Tom Lendacky <thomas.lenda...@amd.com>
Signed-off-by: Sean Christopherson <sea...@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)))

Shouldn't it be !virt_addr_valid() instead of is_vmalloc_addr() ?

                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;

  }