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Date:   Fri, 30 Dec 2022 14:18:46 -0800 (PST)
From:   David Rientjes <rientjes@google.com>
To:     Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>
cc:     Peter Gonda <pgonda@google.com>, Andy Nguyen <theflow@google.com>,
        linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
        John Allen <john.allen@amd.com>,
        Tom Lendacky <thomas.lendacky@amd.com>
Subject: [patch] crypto: ccp - Avoid page allocation failure warning for
 SEV_GET_ID2
In-Reply-To: <826b3dda-5b48-2d42-96b8-c49ccebfdfed@google.com>
Message-ID: <833b4dd0-7f85-b336-0786-965f3f573f74@google.com>
References: <20221214202046.719598-1-pgonda@google.com> <Y5rxd6ZVBqFCBOUT@gondor.apana.org.au> <762d33dc-b5fd-d1ef-848c-7de3a6695557@google.com> <Y6wDJd3hfztLoCp1@gondor.apana.org.au> <826b3dda-5b48-2d42-96b8-c49ccebfdfed@google.com>
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For SEV_GET_ID2, the user provided length does not have a specified 
limitation because the length of the ID may change in the future.  The 
kernel memory allocation, however, is implicitly limited to 4MB on x86 by 
the page allocator, otherwise the kzalloc() will fail.

When this happens, it is best not to spam the kernel log with the warning.  
Simply fail the allocation and return ENOMEM to the user.

Fixes: d6112ea0cb34 ("crypto: ccp - introduce SEV_GET_ID2 command")
Reported-by: Andy Nguyen <theflow@google.com>
Reported-by: Peter Gonda <pgonda@google.com>
Suggested-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David Rientjes <rientjes@google.com>
---
 drivers/crypto/ccp/sev-dev.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -881,7 +881,14 @@ static int sev_ioctl_do_get_id2(struct sev_issue_cmd *argp)
 	input_address = (void __user *)input.address;
 
 	if (input.address && input.length) {
-		id_blob = kzalloc(input.length, GFP_KERNEL);
+		/*
+		 * The length of the ID shouldn't be assumed by software since
+		 * it may change in the future.  The allocation size is limited
+		 * to 1 << (PAGE_SHIFT + MAX_ORDER - 1) by the page allocator.
+		 * If the allocation fails, simply return ENOMEM rather than
+		 * warning in the kernel log.
+		 */
+		id_blob = kzalloc(input.length, GFP_KERNEL | __GFP_NOWARN);
 		if (!id_blob)
 			return -ENOMEM;