[PATCH 3/5] crypto: ccp: Play nice with vmalloc'd memory for SEV command structs

Sean Christopherson
2021-04-02T23:37:35Z

Copy vmalloc'd data to an internal buffer instead of rejecting outright
so that callers can put SEV command buffers on the stack without running
afoul of CONFIG_VMAP_STACK=y. Currently, the largest supported command
takes a 68 byte buffer, i.e. pretty much every command can be put on the
stack. Because sev_cmd_mutex is held for the entirety of a transaction,
only a single bounce buffer is required.

Use a flexible array for the buffer, sized to hold the largest known
command. Alternatively, the buffer could be a union of all known
command structs, but that would incur a higher maintenance cost due to
the need to update the union for every command in addition to updating
the existing sev_cmd_buffer_len().

Align the buffer to an 8-byte boundary, mimicking the alignment that
would be provided by the compiler if any of the structs were embedded
directly. Note, sizeof() correctly incorporates this alignment.

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 | 33 +++++++++++++++++++++++++++------
drivers/crypto/ccp/sev-dev.h | 7 +++++++
2 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 4c513318f16a..6d5882290cfc 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -135,13 +135,14 @@ static int sev_cmd_buffer_len(int cmd)
return 0;
}

-static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
+static int __sev_do_cmd_locked(int cmd, void *__data, int *psp_ret)
{
struct psp_device *psp = psp_master;
struct sev_device *sev;
unsigned int phys_lsb, phys_msb;
unsigned int reg, ret = 0;
int buf_len;
+ void *data;

if (!psp || !psp->sev_data)
return -ENODEV;
@@ -152,11 +153,21 @@ 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))
+ if (WARN_ON_ONCE(!!__data != !!buf_len))
return -EINVAL;

- if (WARN_ON_ONCE(data && is_vmalloc_addr(data)))
- return -EINVAL;
+ if (__data && is_vmalloc_addr(__data)) {
+ /*
+ * If the incoming buffer is virtually allocated, copy it to
+ * the driver's scratch buffer as __pa() will not work for such
+ * addresses, vmalloc_to_page() is not guaranteed to succeed,
+ * and vmalloc'd data may not be physically contiguous.
+ */
+ data = sev->cmd_buf;
+ memcpy(data, __data, buf_len);
+ } else {
+ data = __data;
+ }

/* Get the physical address of the command buffer */
phys_lsb = data ? lower_32_bits(__psp_pa(data)) : 0;
@@ -204,6 +215,13 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
print_hex_dump_debug("(out): ", DUMP_PREFIX_OFFSET, 16, 2, data,
buf_len, false);

+ /*
+ * Copy potential output from the PSP back to __data. Do this even on
+ * failure in case the caller wants to glean something from the error.
+ */
+ if (__data && data != __data)
+ memcpy(__data, data, buf_len);
+
return ret;
}

@@ -978,9 +996,12 @@ int sev_dev_init(struct psp_device *psp)
{
struct device *dev = psp->dev;
struct sev_device *sev;
- int ret = -ENOMEM;
+ int ret = -ENOMEM, cmd_buf_size = 0, i;

- sev = devm_kzalloc(dev, sizeof(*sev), GFP_KERNEL);
+ for (i = 0; i < SEV_CMD_MAX; i++)
+ cmd_buf_size = max(cmd_buf_size, sev_cmd_buffer_len(i));
+
+ sev = devm_kzalloc(dev, sizeof(*sev) + cmd_buf_size, GFP_KERNEL);
if (!sev)
goto e_err;

diff --git a/drivers/crypto/ccp/sev-dev.h b/drivers/crypto/ccp/sev-dev.h
index dd5c4fe82914..b43283ce2d73 100644
--- a/drivers/crypto/ccp/sev-dev.h
+++ b/drivers/crypto/ccp/sev-dev.h
@@ -52,6 +52,13 @@ struct sev_device {
u8 api_major;
u8 api_minor;
u8 build;
+
+ /*
+ * Buffer used for incoming commands whose physical address cannot be
+ * resolved via __pa(), e.g. stack pointers when CONFIG_VMAP_STACK=y.
+ * Note, alignment isn't strictly required.
+ */
+ u8 cmd_buf[] __aligned(8);
};

int sev_dev_init(struct psp_device *psp);
--
2.31.0.208.g409f899ff0-goog