[PATCHv8 07/17] x86/vsyscall: Reorganize the #PF emulation code

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

From: Sohil Mehta <sohil.mehta@intel.com>

Separate out the actual vsyscall emulation from the page fault specific
handling in preparation for the upcoming #GP fault emulation.

No functional change intended.

Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
---
 arch/x86/entry/vsyscall/vsyscall_64.c | 52 ++++++++++++++-------------
 arch/x86/include/asm/vsyscall.h       |  8 ++---
 arch/x86/mm/fault.c                   |  2 +-
 3 files changed, 33 insertions(+), 29 deletions(-)

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index 0b0e0283994f..25f94ac5fd35 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -112,36 +112,13 @@ static bool write_ok_or_segv(unsigned long ptr, size_t size)
 	}
 }
 
-bool emulate_vsyscall(unsigned long error_code,
-		      struct pt_regs *regs, unsigned long address)
+static bool __emulate_vsyscall(struct pt_regs *regs, unsigned long address)
 {
 	unsigned long caller;
 	int vsyscall_nr, syscall_nr, tmp;
 	long ret;
 	unsigned long orig_dx;
 
-	/* Write faults or kernel-privilege faults never get fixed up. */
-	if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
-		return false;
-
-	/* Avoid emulation unless userspace was executing from vsyscall page: */
-	if (address != regs->ip) {
-		/* Failed vsyscall read */
-		if (vsyscall_mode == EMULATE)
-			return false;
-
-		/*
-		 * User code tried and failed to read the vsyscall page.
-		 */
-		warn_bad_vsyscall(KERN_INFO, regs, "vsyscall read attempt denied -- look up the vsyscall kernel parameter if you need a workaround");
-		return false;
-	}
-
-
-	/* X86_PF_INSTR is only set when NX is supported: */
-	if (cpu_feature_enabled(X86_FEATURE_NX))
-		WARN_ON_ONCE(!(error_code & X86_PF_INSTR));
-
 	/*
 	 * No point in checking CS -- the only way to get here is a user mode
 	 * trap to a high address, which means that we're in 64-bit user code.
@@ -274,6 +251,33 @@ bool emulate_vsyscall(unsigned long error_code,
 	return true;
 }
 
+bool emulate_vsyscall_pf(unsigned long error_code, struct pt_regs *regs,
+			 unsigned long address)
+{
+	/* Write faults or kernel-privilege faults never get fixed up. */
+	if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER)
+		return false;
+
+	if (address == regs->ip) {
+		/* X86_PF_INSTR is only set when NX is supported: */
+		if (cpu_feature_enabled(X86_FEATURE_NX))
+			WARN_ON_ONCE(!(error_code & X86_PF_INSTR));
+
+		return __emulate_vsyscall(regs, address);
+	}
+
+	/* Failed vsyscall read */
+	if (vsyscall_mode == EMULATE)
+		return false;
+
+	/*
+	 * User code tried and failed to read the vsyscall page.
+	 */
+	warn_bad_vsyscall(KERN_INFO, regs,
+			  "vsyscall read attempt denied -- look up the vsyscall kernel parameter if you need a workaround");
+	return false;
+}
+
 /*
  * A pseudo VMA to allow ptrace access for the vsyscall page.  This only
  * covers the 64bit vsyscall page now. 32bit has a real VMA now and does
diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h
index 472f0263dbc6..214977f4fa11 100644
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -14,12 +14,12 @@ extern void set_vsyscall_pgtable_user_bits(pgd_t *root);
  * Called on instruction fetch fault in vsyscall page.
  * Returns true if handled.
  */
-extern bool emulate_vsyscall(unsigned long error_code,
-			     struct pt_regs *regs, unsigned long address);
+extern bool emulate_vsyscall_pf(unsigned long error_code,
+				struct pt_regs *regs, unsigned long address);
 #else
 static inline void map_vsyscall(void) {}
-static inline bool emulate_vsyscall(unsigned long error_code,
-				    struct pt_regs *regs, unsigned long address)
+static inline bool emulate_vsyscall_pf(unsigned long error_code,
+				       struct pt_regs *regs, unsigned long address)
 {
 	return false;
 }
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 998bd807fc7b..fbcc2da75fd6 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1316,7 +1316,7 @@ void do_user_addr_fault(struct pt_regs *regs,
 	 * to consider the PF_PK bit.
 	 */
 	if (is_vsyscall_vaddr(address)) {
-		if (emulate_vsyscall(error_code, regs, address))
+		if (emulate_vsyscall_pf(error_code, regs, address))
 			return;
 	}
 #endif
-- 
2.47.2