linux-kernel - [PATCH 08/24] x86/traps: Add C verion of SWITCH_TO_KERNEL_CR3 as switch_to_kernel

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Message-Id: <20210831175025.27570-9-jiangshanlai@gmail.com>
Date:   Wed,  1 Sep 2021 01:50:09 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH 08/24] x86/traps: Add C verion of SWITCH_TO_KERNEL_CR3 as switch_to_kernel_cr3()

From: Lai Jiangshan <laijs@...ux.alibaba.com>

The C version switch_to_kernel_cr3() implements SWITCH_TO_KERNEL_CR3().

No functional difference intended.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 arch/x86/entry/traps.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/arch/x86/entry/traps.c b/arch/x86/entry/traps.c
index ef07ae5fb3a0..9b7d0f15402e 100644
--- a/arch/x86/entry/traps.c
+++ b/arch/x86/entry/traps.c
@@ -765,6 +765,30 @@ struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
 	BUG_ON(!user_mode(&new_stack->regs));
 	return new_stack;
 }
+
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+static __always_inline void pti_switch_to_kernel_cr3(unsigned long user_cr3)
+{
+	/*
+	 * Clear PCID and "PAGE_TABLE_ISOLATION bit", point CR3
+	 * at kernel pagetables:
+	 */
+	unsigned long cr3 = user_cr3 & ~PTI_USER_PGTABLE_AND_PCID_MASK;
+
+	if (static_cpu_has(X86_FEATURE_PCID))
+		cr3 |= X86_CR3_PCID_NOFLUSH;
+
+	native_write_cr3(cr3);
+}
+
+static __always_inline void switch_to_kernel_cr3(void)
+{
+	if (static_cpu_has(X86_FEATURE_PTI))
+		pti_switch_to_kernel_cr3(__native_read_cr3());
+}
+#else
+static __always_inline void switch_to_kernel_cr3(void) {}
+#endif
 #endif
 
 static bool is_sysenter_singlestep(struct pt_regs *regs)
-- 
2.19.1.6.gb485710b