linux-kernel - [patch V2 13/16] x86/tlb: Uninline nmi_uaccess

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Message-Id: <20200421092600.052543007@linutronix.de>
Date:   Tue, 21 Apr 2020 11:20:40 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Christoph Hellwig <hch@....de>,
        Kees Cook <keescook@...omium.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Thomas Lendacky <Thomas.Lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: [patch V2 13/16] x86/tlb: Uninline nmi_uaccess_okay()

cpu_tlbstate is exported because various TLB related functions need access
to it, but cpu_tlbstate is sensitive information which should only be
accessed by well contained kernel functions and not be directly exposed to
modules.

nmi_access_ok() is the last inline function which requires access to
cpu_tlbstate. Move it into the TLB code.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@...cle.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/tlbflush.h |   33 +--------------------------------
 arch/x86/mm/tlb.c               |   32 ++++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 32 deletions(-)

--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -247,38 +247,7 @@ struct tlb_state {
 };
 DECLARE_PER_CPU_SHARED_ALIGNED(struct tlb_state, cpu_tlbstate);
 
-/*
- * Blindly accessing user memory from NMI context can be dangerous
- * if we're in the middle of switching the current user task or
- * switching the loaded mm.  It can also be dangerous if we
- * interrupted some kernel code that was temporarily using a
- * different mm.
- */
-static inline bool nmi_uaccess_okay(void)
-{
-	struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
-	struct mm_struct *current_mm = current->mm;
-
-	VM_WARN_ON_ONCE(!loaded_mm);
-
-	/*
-	 * The condition we want to check is
-	 * current_mm->pgd == __va(read_cr3_pa()).  This may be slow, though,
-	 * if we're running in a VM with shadow paging, and nmi_uaccess_okay()
-	 * is supposed to be reasonably fast.
-	 *
-	 * Instead, we check the almost equivalent but somewhat conservative
-	 * condition below, and we rely on the fact that switch_mm_irqs_off()
-	 * sets loaded_mm to LOADED_MM_SWITCHING before writing to CR3.
-	 */
-	if (loaded_mm != current_mm)
-		return false;
-
-	VM_WARN_ON_ONCE(current_mm->pgd != __va(read_cr3_pa()));
-
-	return true;
-}
-
+bool nmi_uaccess_okay(void);
 #define nmi_uaccess_okay nmi_uaccess_okay
 
 void cr4_update_irqsoff(unsigned long set, unsigned long clear);
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -1079,6 +1079,38 @@ void arch_tlbbatch_flush(struct arch_tlb
 	put_cpu();
 }
 
+/*
+ * Blindly accessing user memory from NMI context can be dangerous
+ * if we're in the middle of switching the current user task or
+ * switching the loaded mm.  It can also be dangerous if we
+ * interrupted some kernel code that was temporarily using a
+ * different mm.
+ */
+bool nmi_uaccess_okay(void)
+{
+	struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
+	struct mm_struct *current_mm = current->mm;
+
+	VM_WARN_ON_ONCE(!loaded_mm);
+
+	/*
+	 * The condition we want to check is
+	 * current_mm->pgd == __va(read_cr3_pa()).  This may be slow, though,
+	 * if we're running in a VM with shadow paging, and nmi_uaccess_okay()
+	 * is supposed to be reasonably fast.
+	 *
+	 * Instead, we check the almost equivalent but somewhat conservative
+	 * condition below, and we rely on the fact that switch_mm_irqs_off()
+	 * sets loaded_mm to LOADED_MM_SWITCHING before writing to CR3.
+	 */
+	if (loaded_mm != current_mm)
+		return false;
+
+	VM_WARN_ON_ONCE(current_mm->pgd != __va(read_cr3_pa()));
+
+	return true;
+}
+
 static ssize_t tlbflush_read_file(struct file *file, char __user *user_buf,
 			     size_t count, loff_t *ppos)
 {