linux-kernel - Re: [PATCH 1/5] crypto: ccp: Detect and reject vmalloc addresses destined for PSP

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Date:   Sun, 4 Apr 2021 08:31:46 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....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 1/5] crypto: ccp: Detect and reject vmalloc addresses
 destined for PSP



Le 03/04/2021 à 01:36, Sean Christopherson a écrit :
> Explicitly reject vmalloc'd data as the source for SEV commands that are
> sent to the PSP.  The PSP works with physical addresses, and __pa() will
> not return the correct address for a vmalloc'd pionter, which at best
> will cause the command to fail, and at worst lead to system instability.
> 
> While it's unlikely that callers will deliberately use vmalloc() for SEV
> buffers, a caller can easily use a vmalloc'd pointer unknowingly when
> running with CONFIG_VMAP_STACK=y as it's not obvious that putting the
> command buffers on the stack would be bad.  The command buffers are
> relative small and easily fit on the stack, and the APIs to do not
> document that the incoming pointer must be a physically contiguous,
> __pa() friendly pointer.
> 
> Cc: Brijesh Singh <brijesh.singh@....com>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Fixes: 200664d5237f ("crypto: ccp: Add Secure Encrypted Virtualization (SEV) command support")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   drivers/crypto/ccp/sev-dev.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index cb9b4c4e371e..6556d220713b 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -150,6 +150,9 @@ 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)))
> +		return -EINVAL;
> +

I hadn't seen this patch when I commented the 2 other ones, I received it only this night.

As commented in the other patches, is_vmalloc_addr() is not the best way to test that __pa() can be 
safely used.

For that, you have virt_addr_valid()

>   	/* Get the physical address of the command buffer */
>   	phys_lsb = data ? lower_32_bits(__psp_pa(data)) : 0;
>   	phys_msb = data ? upper_32_bits(__psp_pa(data)) : 0;
>