linux-kernel - [PATCH PTI v3 01/10] x86/espfix/64: Fix espfix double-fault handling on 5-level systems

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Date:   Tue, 12 Dec 2017 07:56:36 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>, stable@...r.kernel.org,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Dave Hansen <dave.hansen@...el.com>
Subject: [PATCH PTI v3 01/10] x86/espfix/64: Fix espfix double-fault handling on 5-level systems

Using PGDIR_SHIFT to identify espfix64 addresses on 5-level systems
was wrong, and it resulted in panics due to unhandled double faults.
Use P4D_SHIFT instead, which is correct on 4-level and 5-level
machines.

This fixes a panic when running x86 selftests on 5-level machines.

Fixes: 1d33b219563f ("x86/espfix: Add support for 5-level paging")
Cc: stable@...r.kernel.org
Cc: "Kirill A. Shutemov" <kirill@...temov.name>
Cc: Dave Hansen <dave.hansen@...el.com>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/kernel/traps.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 74136fd16f49..c4e5b0a7516f 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -360,7 +360,7 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
 	 *
 	 * No need for ist_enter here because we don't use RCU.
 	 */
-	if (((long)regs->sp >> PGDIR_SHIFT) == ESPFIX_PGD_ENTRY &&
+	if (((long)regs->sp >> P4D_SHIFT) == ESPFIX_PGD_ENTRY &&
 		regs->cs == __KERNEL_CS &&
 		regs->ip == (unsigned long)native_irq_return_iret)
 	{
-- 
2.13.6