linux-kernel - [PATCH 6/8] x86/mm: add vsyscall address helper

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Date:   Fri, 28 Sep 2018 09:02:28 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        sean.j.christopherson@...el.com, peterz@...radead.org,
        tglx@...utronix.de, x86@...nel.org, luto@...nel.org,
        jannh@...gle.com
Subject: [PATCH 6/8] x86/mm: add vsyscall address helper


From: Dave Hansen <dave.hansen@...ux.intel.com>

We will shortly be using this check in two locations.  Put it in
a helper before we do so.

Let's also insert PAGE_MASK instead of the open-coded ~0xfff.
It is easier to read and also more obviously correct considering
the implicit type conversion that has to happen when it is not
an implicit 'unsigned long'.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Sean Christopherson <sean.j.christopherson@...el.com>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: x86@...nel.org
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Jann Horn <jannh@...gle.com>
Cc: Sean Christopherson <sean.j.christopherson@...el.com>
---

 b/arch/x86/mm/fault.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff -puN arch/x86/mm/fault.c~is-vsyscall-addr arch/x86/mm/fault.c
--- a/arch/x86/mm/fault.c~is-vsyscall-addr	2018-09-27 10:17:23.988343565 -0700
+++ b/arch/x86/mm/fault.c	2018-09-27 10:17:23.992343565 -0700
@@ -842,6 +842,15 @@ show_signal_msg(struct pt_regs *regs, un
 	show_opcodes(regs, loglvl);
 }
 
+/*
+ * The (legacy) vsyscall page is the long page in the kernel portion
+ * of the address space that has user-accessible permissions.
+ */
+static bool is_vsyscall_vaddr(unsigned long vaddr)
+{
+	return (vaddr & PAGE_MASK) == VSYSCALL_ADDR;
+}
+
 static void
 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
 		       unsigned long address, u32 *pkey, int si_code)
@@ -871,7 +880,7 @@ __bad_area_nosemaphore(struct pt_regs *r
 		 * emulation.
 		 */
 		if (unlikely((error_code & X86_PF_INSTR) &&
-			     ((address & ~0xfff) == VSYSCALL_ADDR))) {
+			     is_vsyscall_vaddr(address))) {
 			if (emulate_vsyscall(regs, address))
 				return;
 		}
_