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Date: Sat, 3 Dec 2022 13:26:07 +0100
From: Borislav Petkov <bp@...en8.de>
To: Dionna Glaze <dionnaglaze@...gle.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
Peter Gonda <pgonda@...gle.com>,
Thomas Lendacky <Thomas.Lendacky@....com>,
Paolo Bonzini <pbonzini@...hat.com>,
Joerg Roedel <jroedel@...e.de>, Ingo Molnar <mingo@...hat.com>,
Andy Lutomirsky <luto@...nel.org>,
John Allen <john.allen@....com>,
Herbert Xu <herbert@...dor.apana.org.au>,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v8 1/4] crypto: ccp - Name -1 return value as
SEV_RET_NO_FW_CALL
On Fri, Nov 04, 2022 at 11:00:37PM +0000, Dionna Glaze wrote:
> From: Peter Gonda <pgonda@...gle.com>
>
> The PSP can return a "firmware error" code of -1 in circumstances where
> the PSP is not actually called. To make this protocol unambiguous, we
Please use passive voice in your commit message: no "we" or "I", etc,
and describe your changes in imperative mood.
> add a constant naming the return value.
>
> Cc: Thomas Lendacky <Thomas.Lendacky@....com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Joerg Roedel <jroedel@...e.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Andy Lutomirsky <luto@...nel.org>
> Cc: John Allen <john.allen@....com>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: "David S. Miller" <davem@...emloft.net>
>
> Signed-off-by: Peter Gonda <pgonda@...gle.com>
> Signed-off-by: Dionna Glaze <dionnaglaze@...gle.com>
> ---
> drivers/crypto/ccp/sev-dev.c | 2 +-
> include/uapi/linux/psp-sev.h | 7 +++++++
> 2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index 06fc7156c04f..97eb3544ab36 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -444,7 +444,7 @@ static int __sev_platform_init_locked(int *error)
> {
> struct psp_device *psp = psp_master;
> struct sev_device *sev;
> - int rc = 0, psp_ret = -1;
> + int rc = 0, psp_ret = SEV_RET_NO_FW_CALL;
> int (*init_function)(int *error);
>
> if (!psp || !psp->sev_data)
Ok, lemme chase down this flow here:
__sev_platform_init_locked() calls that automatic variable function
pointer ->init_function which already looks funky. See the end of this
mail for a diff removing it and making the code more readable.
The called function can be one of two and both get the pointer to
psp_ret as its only argument.
1. __sev_init_ex_locked() calls __sev_do_cmd_locked() and passes down
*psp_ret.
or
2. __sev_init_locked(). Ditto.
Now, __sev_do_cmd_locked() will overwrite psp_ret when
sev_wait_cmd_ioc() fails. So far so good.
In the case __sev_do_cmd_locked() succeeds, it'll put there something
else:
if (psp_ret)
*psp_ret = reg & PSP_CMDRESP_ERR_MASK;
So no caller will ever see SEV_RET_NO_FW_CALL, as far as I can tell.
And looking further through the rest of the set, nothing tests
SEV_RET_NO_FW_CALL - it only gets assigned.
So why are we even bothering with this?
You can hand in *psp_ret uninitialized and you'll get a value in all
cases. Unless I'm missing an angle.
> diff --git a/include/uapi/linux/psp-sev.h b/include/uapi/linux/psp-sev.h
> index 91b4c63d5cbf..1ad7f0a7e328 100644
> --- a/include/uapi/linux/psp-sev.h
> +++ b/include/uapi/linux/psp-sev.h
> @@ -36,6 +36,13 @@ enum {
> * SEV Firmware status code
> */
> typedef enum {
> + /*
> + * This error code is not in the SEV spec but is added to convey that
> + * there was an error that prevented the SEV Firmware from being called.
> + * This is (u32)-1 since the firmware error code is represented as a
> + * 32-bit integer.
> + */
> + SEV_RET_NO_FW_CALL = 0xffffffff,
What's wrong with having -1 here?
> SEV_RET_SUCCESS = 0,
> SEV_RET_INVALID_PLATFORM_STATE,
> SEV_RET_INVALID_GUEST_STATE,
> --
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 97eb3544ab36..8bc4209b338b 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -440,12 +440,20 @@ static int __sev_init_ex_locked(int *error)
return __sev_do_cmd_locked(SEV_CMD_INIT_EX, &data, error);
}
+static inline int __sev_do_init_locked(int *psp_ret)
+{
+ if (sev_init_ex_buffer)
+ return __sev_init_ex_locked(psp_ret);
+ else
+
+ return __sev_init_locked(psp_ret);
+}
+
static int __sev_platform_init_locked(int *error)
{
struct psp_device *psp = psp_master;
struct sev_device *sev;
- int rc = 0, psp_ret = SEV_RET_NO_FW_CALL;
- int (*init_function)(int *error);
+ int rc = 0, psp_ret;
if (!psp || !psp->sev_data)
return -ENODEV;
@@ -456,15 +464,12 @@ static int __sev_platform_init_locked(int *error)
return 0;
if (sev_init_ex_buffer) {
- init_function = __sev_init_ex_locked;
rc = sev_read_init_ex_file();
if (rc)
return rc;
- } else {
- init_function = __sev_init_locked;
}
- rc = init_function(&psp_ret);
+ rc = __sev_do_init_locked(&psp_ret);
if (rc && psp_ret == SEV_RET_SECURE_DATA_INVALID) {
/*
* Initialization command returned an integrity check failure
@@ -473,9 +478,12 @@ static int __sev_platform_init_locked(int *error)
* initialization function should succeed by replacing the state
* with a reset state.
*/
- dev_err(sev->dev, "SEV: retrying INIT command because of SECURE_DATA_INVALID error. Retrying once to reset PSP SEV state.");
- rc = init_function(&psp_ret);
+ dev_err(sev->dev,
+"SEV: retrying INIT command because of SECURE_DATA_INVALID error. Retrying once to reset PSP SEV state.");
+
+ rc = __sev_do_init_locked(&psp_ret);
}
+
if (error)
*error = psp_ret;
diff --git a/include/uapi/linux/psp-sev.h b/include/uapi/linux/psp-sev.h
index 1ad7f0a7e328..a9ed9e846cd2 100644
--- a/include/uapi/linux/psp-sev.h
+++ b/include/uapi/linux/psp-sev.h
@@ -42,7 +42,7 @@ typedef enum {
* This is (u32)-1 since the firmware error code is represented as a
* 32-bit integer.
*/
- SEV_RET_NO_FW_CALL = 0xffffffff,
+ SEV_RET_NO_FW_CALL = -1,
SEV_RET_SUCCESS = 0,
SEV_RET_INVALID_PLATFORM_STATE,
SEV_RET_INVALID_GUEST_STATE,
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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