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

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Message-ID: <bc82825c-03ff-1b3f-7166-f6e5671f0a4f@amd.com>
Date:   Mon, 5 Apr 2021 11:26:01 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        John Allen <john.allen@....com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 2/5] crypto: ccp: Reject SEV commands with mismatching
 command buffer

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@....com>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.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;
>  }
>