linux-kernel - [PATCH] x86/resctrl: avoid divide by 0 num

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <20250721180051.3645697-1-brho@google.com>
Date: Mon, 21 Jul 2025 18:00:47 +0000
From: Barret Rhoden <brho@...gle.com>
To: Tony Luck <tony.luck@...el.com>, Reinette Chatre <reinette.chatre@...el.com>
Cc: Dave Martin <Dave.Martin@....com>, James Morse <james.morse@....com>, 
	linux-kernel@...r.kernel.org
Subject: [PATCH] x86/resctrl: avoid divide by 0 num_rmid

x86_cache_max_rmid's default is -1.  If the hardware or VM doesn't set
the right cpuid bits, num_rmid can be 0.

Signed-off-by: Barret Rhoden <brho@...gle.com>

---
I ran into this on a VM on granite rapids.  I guess the VMM told the
kernel it was a GNR, but didn't set all the cache/rsctl bits.

 arch/x86/kernel/cpu/resctrl/monitor.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index c261558276cd..226dee05f96e 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -359,6 +359,12 @@ int __init rdt_get_mon_l3_config(struct rdt_resource *r)
 	else if (mbm_offset > MBM_CNTR_WIDTH_OFFSET_MAX)
 		pr_warn("Ignoring impossible MBM counter offset\n");
 
+	if (r->num_rmid < 1) {
+		pr_warn("Invalid num_rmid %d, cach_max_rmid was %d\n",
+			r->num_rmid, boot_cpu_data.x86_cache_max_rmid);
+		r->num_rmid = 1;
+	}
+
 	/*
 	 * A reasonable upper limit on the max threshold is the number
 	 * of lines tagged per RMID if all RMIDs have the same number of
-- 
2.50.0.727.gbf7dc18ff4-goog