[PATCH v2 1/3] x86_64,vsyscall: Turn vsyscalls all the way off when vsyscall=none

From: Andy Lutomirski
Date: Wed Oct 29 2014 - 17:34:01 EST


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.

Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
---
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 419e83b58436..2d912629c96e 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -307,6 +307,8 @@ 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;
}

@@ -327,7 +329,7 @@ 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;
}

void __init map_vsyscall(void)
@@ -335,10 +337,12 @@ 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);
}
--
1.9.3

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