linux-kernel - [RFC 07/10] hv: Use free_decrypted

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Message-Id: <20231017202505.340906-8-rick.p.edgecombe@intel.com>
Date:   Tue, 17 Oct 2023 13:25:02 -0700
From:   Rick Edgecombe <rick.p.edgecombe@...el.com>
To:     x86@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, luto@...nel.org,
        peterz@...radead.org, kirill.shutemov@...ux.intel.com,
        elena.reshetova@...el.com, isaku.yamahata@...el.com,
        seanjc@...gle.com, Michael Kelley <mikelley@...rosoft.com>,
        thomas.lendacky@....com, decui@...rosoft.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Cc:     rick.p.edgecombe@...el.com, "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, linux-hyperv@...r.kernel.org
Subject: [RFC 07/10] hv: Use free_decrypted_pages()

On TDX it is possible for the untrusted host to cause
set_memory_encrypted() or set_memory_decrypted() to fail such that an
error is returned and the resulting memory is shared. Callers need to take
care to handle these errors to avoid returning decrypted (shared) memory to
the page allocator, which could lead to functional or security issues.

Hyperv could free decrypted/shared pages if set_memory_decrypted() fails.
Use the recently added free_decrypted_pages() to avoid this.

Only compile tested.

Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
Cc: Haiyang Zhang <haiyangz@...rosoft.com>
Cc: Wei Liu <wei.liu@...nel.org>
Cc: Dexuan Cui <decui@...rosoft.com>
Cc: linux-hyperv@...r.kernel.org
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
---
 drivers/hv/channel.c    |  7 ++++---
 drivers/hv/connection.c | 13 +++++++++----
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 56f7e06c673e..1ad8f7fabe06 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -153,9 +153,10 @@ void vmbus_free_ring(struct vmbus_channel *channel)
 	hv_ringbuffer_cleanup(&channel->inbound);
 
 	if (channel->ringbuffer_page) {
-		__free_pages(channel->ringbuffer_page,
-			     get_order(channel->ringbuffer_pagecount
-				       << PAGE_SHIFT));
+		int order = get_order(channel->ringbuffer_pagecount << PAGE_SHIFT);
+		unsigned long addr = (unsigned long)page_address(channel->ringbuffer_page);
+
+		free_decrypted_pages(addr, order);
 		channel->ringbuffer_page = NULL;
 	}
 }
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 3cabeeabb1ca..cffad9b139d3 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -315,6 +315,7 @@ int vmbus_connect(void)
 
 void vmbus_disconnect(void)
 {
+	int ret;
 	/*
 	 * First send the unload request to the host.
 	 */
@@ -337,11 +338,15 @@ void vmbus_disconnect(void)
 		vmbus_connection.int_page = NULL;
 	}
 
-	set_memory_encrypted((unsigned long)vmbus_connection.monitor_pages[0], 1);
-	set_memory_encrypted((unsigned long)vmbus_connection.monitor_pages[1], 1);
+	ret = set_memory_encrypted((unsigned long)vmbus_connection.monitor_pages[0], 1);
+	ret |= set_memory_encrypted((unsigned long)vmbus_connection.monitor_pages[1], 1);
 
-	hv_free_hyperv_page(vmbus_connection.monitor_pages[0]);
-	hv_free_hyperv_page(vmbus_connection.monitor_pages[1]);
+	if (!ret) {
+		hv_free_hyperv_page(vmbus_connection.monitor_pages[0]);
+		hv_free_hyperv_page(vmbus_connection.monitor_pages[1]);
+	} else {
+		WARN_ONCE(1, "Failed to re-encrypt memory before freeing, leaking pages!\n");
+	}
 	vmbus_connection.monitor_pages[0] = NULL;
 	vmbus_connection.monitor_pages[1] = NULL;
 }
-- 
2.34.1