linux-kernel - [tip: x86/fred] x86/fred: Add a NMI entry stub for FRED

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

Date: Thu, 25 Jan 2024 18:21:23 -0000
From: "tip-bot2 for H. Peter Anvin (Intel)" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "H. Peter Anvin (Intel)" <hpa@...or.com>, Xin Li <xin3.li@...el.com>,
 Thomas Gleixner <tglx@...utronix.de>, Shan Kang <shan.kang@...el.com>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/fred] x86/fred: Add a NMI entry stub for FRED

The following commit has been merged into the x86/fred branch of tip:

Commit-ID:     994f75798425ca0865b54dcc7bbe13bba5e4cfe4
Gitweb:        https://git.kernel.org/tip/994f75798425ca0865b54dcc7bbe13bba5e4cfe4
Author:        H. Peter Anvin (Intel) <hpa@...or.com>
AuthorDate:    Fri, 15 Dec 2023 22:31:39 -08:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Thu, 25 Jan 2024 19:10:32 +01:00

x86/fred: Add a NMI entry stub for FRED

On a FRED system, NMIs nest both with themselves and faults, transient
information is saved into the stack frame, and NMI unblocking only
happens when the stack frame indicates that so should happen.

Thus, the NMI entry stub for FRED is really quite small...

Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
Signed-off-by: Xin Li <xin3.li@...el.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Shan Kang <shan.kang@...el.com>
Link: https://lore.kernel.org/r/20231216063139.25567-1-xin3.li@intel.com

---
 arch/x86/kernel/nmi.c | 42 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 42 insertions(+)

diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 17e955a..3130a66 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -35,6 +35,7 @@
 #include <asm/nospec-branch.h>
 #include <asm/microcode.h>
 #include <asm/sev.h>
+#include <asm/fred.h>

 #define CREATE_TRACE_POINTS
 #include <trace/events/nmi.h>
@@ -651,6 +652,47 @@ void nmi_backtrace_stall_check(const struct cpumask *btp)

 #endif

+#ifdef CONFIG_X86_FRED
+/*
+ * With FRED, CR2/DR6 is pushed to #PF/#DB stack frame during FRED
+ * event delivery, i.e., there is no problem of transient states.
+ * And NMI unblocking only happens when the stack frame indicates
+ * that so should happen.
+ *
+ * Thus, the NMI entry stub for FRED is really straightforward and
+ * as simple as most exception handlers. As such, #DB is allowed
+ * during NMI handling.
+ */
+DEFINE_FREDENTRY_NMI(exc_nmi)
+{
+	irqentry_state_t irq_state;
+
+	if (arch_cpu_is_offline(smp_processor_id())) {
+		if (microcode_nmi_handler_enabled())
+			microcode_offline_nmi_handler();
+		return;
+	}
+
+	/*
+	 * Save CR2 for eventual restore to cover the case where the NMI
+	 * hits the VMENTER/VMEXIT region where guest CR2 is life. This
+	 * prevents guest state corruption in case that the NMI handler
+	 * takes a page fault.
+	 */
+	this_cpu_write(nmi_cr2, read_cr2());
+
+	irq_state = irqentry_nmi_enter(regs);
+
+	inc_irq_stat(__nmi_count);
+	default_do_nmi(regs);
+
+	irqentry_nmi_exit(regs, irq_state);
+
+	if (unlikely(this_cpu_read(nmi_cr2) != read_cr2()))
+		write_cr2(this_cpu_read(nmi_cr2));
+}
+#endif
+
 void stop_nmi(void)
 {
 	ignore_nmis++;