x86-64: Set siginfo and context on vsyscall emulation faults

To make this work, we teach the page fault handler how to send
signals on failed uaccess.  This only works for user addresses
(kernel addresses will never hit the page fault handler in the
first place), so we need to generate signals for those
separately.

This gets the tricky case right: if the user buffer spans
multiple pages and only the second page is invalid, we set
cr2 and si_addr correctly.  UML relies on this behavior to
"fault in" pages as needed.

We steal a bit from thread_info.uaccess_err to enable this.
Before this change, uaccess_err was a 32-bit boolean value.

This fixes issues with UML when vsyscall=emulate.

Reported-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: richard -rw- weinberger <richard.weinberger@gmail.com>
Cc: H. Peter Anvin <hpa@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/4c8f91de7ec5cd2ef0f59521a04e1015f11e42b4.1320712291.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 17 insertions, 7 deletions

diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index d0474ad2a6e5..1fb85dbe390a 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -25,7 +25,7 @@ int fixup_exception(struct pt_regs *regs)
         if (fixup) {
                 /* If fixup is less than 16, it means uaccess error */
                 if (fixup->fixup < 16) {
-                        current_thread_info()->uaccess_err = -EFAULT;
+                        current_thread_info()->uaccess_err = 1;
                         regs->ip += fixup->fixup;
                         return 1;
                 }
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 5db0490deb07..9d74824a708d 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -626,7 +626,7 @@ pgtable_bad(struct pt_regs *regs, unsigned long error_code,
 
 static noinline void
 no_context(struct pt_regs *regs, unsigned long error_code,
-           unsigned long address)
+           unsigned long address, int signal, int si_code)
 {
         struct task_struct *tsk = current;
         unsigned long *stackend;
@@ -634,8 +634,17 @@ no_context(struct pt_regs *regs, unsigned long error_code,
         int sig;
 
         /* Are we prepared to handle this kernel fault? */
-        if (fixup_exception(regs))
+        if (fixup_exception(regs)) {
+                if (current_thread_info()->sig_on_uaccess_error && signal) {
+                        tsk->thread.trap_no = 14;
+                        tsk->thread.error_code = error_code | PF_USER;
+                        tsk->thread.cr2 = address;
+
+                        /* XXX: hwpoison faults will set the wrong code. */
+                        force_sig_info_fault(signal, si_code, address, tsk, 0);
+                }
                 return;
+        }
 
         /*
          * 32-bit:
@@ -755,7 +764,7 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
         if (is_f00f_bug(regs, address))
                 return;
 
-        no_context(regs, error_code, address);
+        no_context(regs, error_code, address, SIGSEGV, si_code);
 }
 
 static noinline void
@@ -819,7 +828,7 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
 
         /* Kernel mode? Handle exceptions or die: */
         if (!(error_code & PF_USER)) {
-                no_context(regs, error_code, address);
+                no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
                 return;
         }
 
@@ -854,7 +863,7 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code,
                 if (!(fault & VM_FAULT_RETRY))
                         up_read(&current->mm->mmap_sem);
                 if (!(error_code & PF_USER))
-                        no_context(regs, error_code, address);
+                        no_context(regs, error_code, address, 0, 0);
                 return 1;
         }
         if (!(fault & VM_FAULT_ERROR))
@@ -864,7 +873,8 @@ mm_fault_error(struct pt_regs *regs, unsigned long error_code,
                 /* Kernel mode? Handle exceptions or die: */
                 if (!(error_code & PF_USER)) {
                         up_read(&current->mm->mmap_sem);
-                        no_context(regs, error_code, address);
+                        no_context(regs, error_code, address,
+                                   SIGSEGV, SEGV_MAPERR);
                         return 1;
                 }