x86/sgx: Fix deadlock in SGX NUMA node search

JIRA: https://issues.redhat.com/browse/RHEL-22826
JIRA: https://issues.redhat.com/browse/RHEL-63522
CVE: CVE-2024-49856
Upstream Status: merged into the linux.git

commit 9c93684
Author: Aaron Lu <aaron.lu@intel.com>
Date:   Thu Sep 5 16:08:54 2024 +0800

    x86/sgx: Fix deadlock in SGX NUMA node search

    When the current node doesn't have an EPC section configured by firmware
    and all other EPC sections are used up, CPU can get stuck inside the
    while loop that looks for an available EPC page from remote nodes
    indefinitely, leading to a soft lockup. Note how nid_of_current will
    never be equal to nid in that while loop because nid_of_current is not
    set in sgx_numa_mask.

    Also worth mentioning is that it's perfectly fine for the firmware not
    to setup an EPC section on a node. While setting up an EPC section on
    each node can enhance performance, it is not a requirement for
    functionality.

    Rework the loop to start and end on *a* node that has SGX memory. This
    avoids the deadlock looking for the current SGX-lacking node to show up
    in the loop when it never will.

    Fixes: 901ddbb ("x86/sgx: Add a basic NUMA allocation scheme to sgx_alloc_epc_page()")
    Reported-by: "Molina Sabido, Gerardo" <gerardo.molina.sabido@intel.com>
    Signed-off-by: Aaron Lu <aaron.lu@intel.com>
    Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
    Reviewed-by: Kai Huang <kai.huang@intel.com>
    Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
    Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
    Tested-by: Zhimin Luo <zhimin.luo@intel.com>
    Link: https://lore.kernel.org/all/20240905080855.1699814-2-aaron.lu%40intel.com

Signed-off-by: Vladis Dronov <vdronov@redhat.com>

Author: nefigtut

arch/x86/kernel/cpu/sgx/main.c

@@ -474,24 +474,25 @@ struct sgx_epc_page *__sgx_alloc_epc_page(void)
 {
 	struct sgx_epc_page *page;
 	int nid_of_current = numa_node_id();
-	int nid = nid_of_current;
+	int nid_start, nid;
 
-	if (node_isset(nid_of_current, sgx_numa_mask)) {
-		page = __sgx_alloc_epc_page_from_node(nid_of_current);
-		if (page)
-			return page;
-	}
-
-	/* Fall back to the non-local NUMA nodes: */
-	while (true) {
-		nid = next_node_in(nid, sgx_numa_mask);
-		if (nid == nid_of_current)
-			break;
+	/*
+	 * Try local node first. If it doesn't have an EPC section,
+	 * fall back to the non-local NUMA nodes.
+	 */
+	if (node_isset(nid_of_current, sgx_numa_mask))
+		nid_start = nid_of_current;
+	else
+		nid_start = next_node_in(nid_of_current, sgx_numa_mask);
 
+	nid = nid_start;
+	do {
 		page = __sgx_alloc_epc_page_from_node(nid);
 		if (page)
 			return page;
-	}
+
+		nid = next_node_in(nid, sgx_numa_mask);
+	} while (nid != nid_start);
 
 	return ERR_PTR(-ENOMEM);
 }