linux-kernel - [PATCH 2/3] x86_64,vsyscall: Turn vsyscalls all the way off when vsyscall=none

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Message-Id: <00157d645245f5476d0177d853a9c5c0dc7efb2b.1400797362.git.luto@amacapital.net>
Date:	Thu, 22 May 2014 15:24:15 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>
Subject: [PATCH 2/3] x86_64,vsyscall: Turn vsyscalls all the way off when vsyscall=none

I see no point in having an unusable read-only page sitting at
0xffffffffff600000 when vsyscall=none.  Instead, skip mapping it and
remove it from /proc/PID/maps.

I kept the ratelimited warning when programs try to use a vsyscall
in this mode, since it may help admins avoid confusion.

Signed-off-by: Andy Lutomirski <luto@...capital.net>
---
 arch/x86/kernel/vsyscall_64.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index ad84894..8d38eb5 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -309,6 +309,8 @@ struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
 	if (!mm || mm->context.ia32_compat)
 		return NULL;
 #endif
+	if (vsyscall_mode == NONE)
+		return NULL;
 	return &gate_vma;
 }
 
@@ -329,7 +331,7 @@ int in_gate_area(struct mm_struct *mm, unsigned long addr)
  */
 int in_gate_area_no_mm(unsigned long addr)
 {
-	return (addr & PAGE_MASK) == VSYSCALL_ADDR;
+	return vsyscall_mode != NONE && (addr & PAGE_MASK) == VSYSCALL_ADDR;
 }
 
 /*
@@ -380,10 +382,12 @@ void __init map_vsyscall(void)
 	extern char __vsyscall_page;
 	unsigned long physaddr_vsyscall = __pa_symbol(&__vsyscall_page);
 
-	__set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
-		     vsyscall_mode == NATIVE
-		     ? PAGE_KERNEL_VSYSCALL
-		     : PAGE_KERNEL_VVAR);
+	if (vsyscall_mode != NONE)
+		__set_fixmap(VSYSCALL_PAGE, physaddr_vsyscall,
+			     vsyscall_mode == NATIVE
+			     ? PAGE_KERNEL_VSYSCALL
+			     : PAGE_KERNEL_VVAR);
+
 	BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
 		     (unsigned long)VSYSCALL_ADDR);
 }
-- 
1.9.0

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