linux-kernel - [PATCH] crypto/ccp: Fix locking on alloc failure handling

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Message-ID: <20250617094354.1357771-1-aik@amd.com>
Date: Tue, 17 Jun 2025 19:43:54 +1000
From: Alexey Kardashevskiy <aik@....com>
To: <linux-crypto@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, Ashish Kalra <ashish.kalra@....com>, "Tom
 Lendacky" <thomas.lendacky@....com>, John Allen <john.allen@....com>,
	"Herbert Xu" <herbert@...dor.apana.org.au>, "Borislav Petkov (AMD)"
	<bp@...en8.de>, Michael Roth <michael.roth@....com>, Alexey Kardashevskiy
	<aik@....com>
Subject: [PATCH] crypto/ccp: Fix locking on alloc failure handling

The __snp_alloc_firmware_pages() helper allocates pages in the firmware
state (alloc + rmpupdate). In case of failed rmpupdate, it tries
reclaiming pages with already changed state. This requires calling
the PSP firmware and since there is sev_cmd_mutex to guard such calls,
the helper takes a "locked" parameter so specify if the lock needs to
be held.

Most calls happen from snp_alloc_firmware_page() which executes without
the lock. However

commit 24512afa4336 ("crypto: ccp: Handle the legacy TMR allocation when SNP is enabled")

switched sev_fw_alloc() from alloc_pages() (which does not call the PSP) to
__snp_alloc_firmware_pages() (which does) but did not account for the fact
that sev_fw_alloc() is called from __sev_platform_init_locked()
(via __sev_platform_init_handle_tmr()) and executes with the lock held.

Add a "locked" parameter to __snp_alloc_firmware_pages().
Make sev_fw_alloc() use the new parameter to prevent potential deadlock in
rmp_mark_pages_firmware() if rmpupdate() failed.

Fixes: 24512afa4336 ("crypto: ccp: Handle the legacy TMR allocation when SNP is enabled")
Signed-off-by: Alexey Kardashevskiy <aik@....com>
---
 drivers/crypto/ccp/sev-dev.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 3451bada884e..16a11d5efe46 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -434,7 +434,7 @@ static int rmp_mark_pages_firmware(unsigned long paddr, unsigned int npages, boo
 	return rc;
 }
 
-static struct page *__snp_alloc_firmware_pages(gfp_t gfp_mask, int order)
+static struct page *__snp_alloc_firmware_pages(gfp_t gfp_mask, int order, bool locked)
 {
 	unsigned long npages = 1ul << order, paddr;
 	struct sev_device *sev;
@@ -453,7 +453,7 @@ static struct page *__snp_alloc_firmware_pages(gfp_t gfp_mask, int order)
 		return page;
 
 	paddr = __pa((unsigned long)page_address(page));
-	if (rmp_mark_pages_firmware(paddr, npages, false))
+	if (rmp_mark_pages_firmware(paddr, npages, locked))
 		return NULL;
 
 	return page;
@@ -463,7 +463,7 @@ void *snp_alloc_firmware_page(gfp_t gfp_mask)
 {
 	struct page *page;
 
-	page = __snp_alloc_firmware_pages(gfp_mask, 0);
+	page = __snp_alloc_firmware_pages(gfp_mask, 0, false);
 
 	return page ? page_address(page) : NULL;
 }
@@ -498,7 +498,7 @@ static void *sev_fw_alloc(unsigned long len)
 {
 	struct page *page;
 
-	page = __snp_alloc_firmware_pages(GFP_KERNEL, get_order(len));
+	page = __snp_alloc_firmware_pages(GFP_KERNEL, get_order(len), true);
 	if (!page)
 		return NULL;
 
-- 
2.49.0