Re: [PATCH V3 1/4] crypto: ccp - Fix SEV_INIT error logging on init

[Sean Christopherson <seanjc@google.com>]

On Tue, Nov 02, 2021, Peter Gonda wrote:
> Currently only the firmware error code is printed. This is incomplete
> and also incorrect as error cases exists where the firmware is never
> called and therefore does not set an error code. This change zeros the
> firmware error code in case the call does not get that far and prints
> the return code for non firmware errors.
> 
> Signed-off-by: Peter Gonda <pgonda@google.com>
> Reviewed-by: Marc Orr <marcorr@google.com>
> Acked-by: David Rientjes <rientjes@google.com>
> Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Cc: Marc Orr <marcorr@google.com>
> Cc: Joerg Roedel <jroedel@suse.de>
> Cc: Herbert Xu <herbert@gondor.apana.org.au>
> Cc: David Rientjes <rientjes@google.com>
> Cc: John Allen <john.allen@amd.com>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: linux-crypto@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> ---
>  drivers/crypto/ccp/sev-dev.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index 2ecb0e1f65d8..ec89a82ba267 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -1065,7 +1065,7 @@ void sev_pci_init(void)
>  {
>  	struct sev_device *sev = psp_master->sev_data;
>  	struct page *tmr_page;
> -	int error, rc;
> +	int error = 0, rc;

Wouldn't it be more appropriate to use something the PSP can't return, e.g. -1?
'0' is SEV_RET_SUCCESS, which is quite misleading, e.g. the below error message
will print

	SEV: failed to INIT error 0, rc -16

which a bit head scratching without looking at the code.  AFAICT, the PSP return
codes aren't intrinsically hex, so printing error as a signed demical and thus

	SEV: failed to INIT error -1, rc -16

would be less confusing.

And IMO requiring the caller to initialize error is will be neverending game of
whack-a-mole.  E.g. sev_ioctl() fails to set "error" in the userspace structure,
and literally every function exposed via include/linux/psp-sev.h has this same
issue.  Case in point, the retry path fails to re-initialize "error" and will
display stale information if the second sev_platform_init() fails without reaching
the PSP.

	rc = sev_platform_init(&error);
	if (rc && (error == SEV_RET_SECURE_DATA_INVALID)) {
		/*
		 * INIT command returned an integrity check failure
		 * status code, meaning that firmware load and
		 * validation of SEV related persistent data has
		 * failed and persistent state has been erased.
		 * Retrying INIT command here should succeed.
		 */
		dev_dbg(sev->dev, "SEV: retrying INIT command");
		rc = sev_platform_init(&error); <------ error may or may not be set
	}

Ideally, error wouldn't be an output param and instead would be squished into the
true return value, but that'd required quite the refactoring, and might yield ugly
code generation on non-64-bit architectures (does this code support those?).

As a minimal step toward sanity, sev_ioctl(), __sev_platform_init_locked(), and
__sev_do_cmd_locked() should initialize the incoming error.  Long term, sev-dev
really needs to either have well-defined API for when "error" is meaningful, or
ensure the pointer is initialized in all paths.

E.g. 

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index ec89a82ba267..549686a1e812 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -149,6 +149,9 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
        unsigned int reg, ret = 0;
        int buf_len;

+       if (psp_ret)
+               *psp_ret = -1;
+
        if (!psp || !psp->sev_data)
                return -ENODEV;

@@ -192,9 +195,6 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
        /* wait for command completion */
        ret = sev_wait_cmd_ioc(sev, &reg, psp_timeout);
        if (ret) {
-               if (psp_ret)
-                       *psp_ret = 0;
-
                dev_err(sev->dev, "sev command %#x timed out, disabling PSP\n", cmd);
                psp_dead = true;

@@ -243,6 +243,9 @@ static int __sev_platform_init_locked(int *error)
        struct sev_device *sev;
        int rc = 0;

+       if (error)
+               *error = -1;
+
        if (!psp || !psp->sev_data)
                return -ENODEV;

@@ -838,6 +841,8 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
        if (input.cmd > SEV_MAX)
                return -EINVAL;

+       input.error = -1;
+
        mutex_lock(&sev_cmd_mutex);

        switch (input.cmd) {

>  	if (!sev)
>  		return;
> @@ -1104,7 +1104,8 @@ void sev_pci_init(void)
>  	}
>  
>  	if (rc) {
> -		dev_err(sev->dev, "SEV: failed to INIT error %#x\n", error);
> +		dev_err(sev->dev, "SEV: failed to INIT error %#x, rc %d\n",
> +			error, rc);
>  		return;
>  	}
>  
> -- 
> 2.33.1.1089.g2158813163f-goog
>