Re: [PATCH 2/2] virt: tdx-guest: Allocate Quote buffer dynamically

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Unbounded host-provided quote size causes guest kernel warning (and potential panic) during allocation.
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commit 918e9fdc48e5a03b41dab3a999be1a3f631327c1
Author: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

virt: tdx-guest: Allocate Quote buffer dynamically

This commit modifies the TDX attestation driver to allocate the Quote
buffer dynamically based on the size reported by the TDX module. It falls
back to a default 128 KB buffer if the reported size is unavailable,
supporting larger quotes needed for newer schemes.

> diff --git a/drivers/virt/coco/tdx-guest/tdx-guest.c b/drivers/virt/coco/tdx-guest/tdx-guest.c
> --- a/drivers/virt/coco/tdx-guest/tdx-guest.c
> +++ b/drivers/virt/coco/tdx-guest/tdx-guest.c
[ ... ]
> @@ -223,19 +223,43 @@ static void free_quote_buf(void *buf)
>  	free_pages_exact(buf, len);
>  }
>  
> -static void *alloc_quote_buf(void)
> +static size_t get_quote_buf_size(void)
>  {
> -	size_t len = PAGE_ALIGN(GET_QUOTE_BUF_SIZE);
> -	unsigned int count = len >> PAGE_SHIFT;
> +	size_t buf_sz = GET_QUOTE_DEFAULT_BUF_SIZE;
> +	u32 quote_sz;
> +
> +	quote_sz = tdx_get_max_quote_size();
> +
> +	if (quote_sz)
> +		/* Reported size does not include GetQuote header */
> +		buf_sz = TDX_QUOTE_BUF_LEN(quote_sz);
> +
> +	return PAGE_ALIGN(buf_sz);
> +}
> +
> +static void *alloc_quote_buf(size_t *buflen)
> +{
> +	unsigned int count;
> +	size_t len;
>  	void *addr;
>  
> +	len = get_quote_buf_size();
> +
> +	/*
> +	 * This fails if the requested size exceeds the buddy allocator's
> +	 * maximum order (order-10, 4MB).
> +	 */
>  	addr = alloc_pages_exact(len, GFP_KERNEL | __GFP_ZERO);

[Severity: High]
If the host provides an excessively large quote_sz, could this allocation
trigger a kernel warning?

The comments indicate the buddy allocator will fail requests exceeding
its maximum order. However, passing an unbounded, host-controlled size
directly to alloc_pages_exact() without __GFP_NOWARN will trigger a
WARN_ON_ONCE_GFP in the page allocator's slow path before failing.

If a host is malicious or misconfigured, could this be used to spam the
guest's kernel log or cause a denial-of-service crash if the guest runs
with panic_on_warn=1?

Would it be better to explicitly check the size against a reasonable upper
bound or include the __GFP_NOWARN flag here?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260612110853.3188196-1-peter.fang@intel.com?part=2