[PATCH AUTOSEL 5.10 06/10] x86/boot: Ignore NMIs during very early boot

[Sasha Levin]

From: Jun'ichi Nomura <junichi.nomura@xxxxxxx>

[ Upstream commit 78a509fba9c9b1fcb77f95b7c6be30da3d24823a ]

When there are two racing NMIs on x86, the first NMI invokes NMI handler and
the 2nd NMI is latched until IRET is executed.

If panic on NMI and panic kexec are enabled, the first NMI triggers
panic and starts booting the next kernel via kexec. Note that the 2nd
NMI is still latched. During the early boot of the next kernel, once
an IRET is executed as a result of a page fault, then the 2nd NMI is
unlatched and invokes the NMI handler.

However, NMI handler is not set up at the early stage of boot, which
results in a boot failure.

Avoid such problems by setting up a NOP handler for early NMIs.

[ mingo: Refined the changelog. ]

Signed-off-by: Jun'ichi Nomura <junichi.nomura@xxxxxxx>
Signed-off-by: Derek Barbosa <debarbos@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/x86/boot/compressed/ident_map_64.c    | 5 +++++
 arch/x86/boot/compressed/idt_64.c          | 1 +
 arch/x86/boot/compressed/idt_handlers_64.S | 1 +
 arch/x86/boot/compressed/misc.h            | 1 +
 4 files changed, 8 insertions(+)

diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index f4a2e6d373b2..1e4eb3894ec4 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -367,3 +367,8 @@ void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
 	 */
 	add_identity_map(address, end);
 }
+
+void do_boot_nmi_trap(struct pt_regs *regs, unsigned long error_code)
+{
+	/* Empty handler to ignore NMI during early boot */
+}
diff --git a/arch/x86/boot/compressed/idt_64.c b/arch/x86/boot/compressed/idt_64.c
index 804a502ee0d2..eb30bb20c33b 100644
--- a/arch/x86/boot/compressed/idt_64.c
+++ b/arch/x86/boot/compressed/idt_64.c
@@ -45,6 +45,7 @@ void load_stage2_idt(void)
 	boot_idt_desc.address = (unsigned long)boot_idt;
 
 	set_idt_entry(X86_TRAP_PF, boot_page_fault);
+	set_idt_entry(X86_TRAP_NMI, boot_nmi_trap);
 
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 	set_idt_entry(X86_TRAP_VC, boot_stage2_vc);
diff --git a/arch/x86/boot/compressed/idt_handlers_64.S b/arch/x86/boot/compressed/idt_handlers_64.S
index 22890e199f5b..4d03c8562f63 100644
--- a/arch/x86/boot/compressed/idt_handlers_64.S
+++ b/arch/x86/boot/compressed/idt_handlers_64.S
@@ -70,6 +70,7 @@ SYM_FUNC_END(\name)
 	.code64
 
 EXCEPTION_HANDLER	boot_page_fault do_boot_page_fault error_code=1
+EXCEPTION_HANDLER	boot_nmi_trap do_boot_nmi_trap error_code=0
 
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 EXCEPTION_HANDLER	boot_stage1_vc do_vc_no_ghcb		error_code=1
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index d9a631c5973c..0ccc32718483 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -156,6 +156,7 @@ extern struct desc_ptr boot_idt_desc;
 
 /* IDT Entry Points */
 void boot_page_fault(void);
+void boot_nmi_trap(void);
 void boot_stage1_vc(void);
 void boot_stage2_vc(void);
 
-- 
2.43.0