path: root/arch/parisc/mm/fault.c
diff options
authorHelge Deller <deller@gmx.de>2017-03-25 11:59:15 +0100
committerHelge Deller <deller@gmx.de>2017-03-29 21:50:36 +0200
commitd19f5e41b344a057bb2450024a807476f30978d2 (patch)
tree4f7f4fa52e5e845ec0abe38d1906404d575ca8ab /arch/parisc/mm/fault.c
parentparisc: Fix access fault handling in pa_memcpy() (diff)
parisc: Clean up fixup routines for get_user()/put_user()
Al Viro noticed that userspace accesses via get_user()/put_user() can be simplified a lot with regard to usage of the exception handling. This patch implements a fixup routine for get_user() and put_user() in such that the exception handler will automatically load -EFAULT into the register %r8 (the error value) in case on a fault on userspace. Additionally the fixup routine will zero the target register on fault in case of a get_user() call. The target register is extracted out of the faulting assembly instruction. This patch brings a few benefits over the old implementation: 1. Exception handling gets much cleaner, easier and smaller in size. 2. Helper functions like fixup_get_user_skip_1 (all of fixup.S) can be dropped. 3. No need to hardcode %r9 as target register for get_user() any longer. This helps the compiler register allocator and thus creates less assembler statements. 4. No dependency on the exception_data contents any longer. 5. Nested faults will be handled cleanly. Reported-by: Al Viro <viro@ZenIV.linux.org.uk> Cc: <stable@vger.kernel.org> # v4.9+ Signed-off-by: Helge Deller <deller@gmx.de>
Diffstat (limited to '')
1 files changed, 17 insertions, 0 deletions
diff --git a/arch/parisc/mm/fault.c b/arch/parisc/mm/fault.c
index deab89a8915a..32ec22146141 100644
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -150,6 +150,23 @@ int fixup_exception(struct pt_regs *regs)
d->fault_space = regs->isr;
d->fault_addr = regs->ior;
+ /*
+ * Fix up get_user() and put_user().
+ * ASM_EXCEPTIONTABLE_ENTRY_EFAULT() sets the least-significant
+ * bit in the relative address of the fixup routine to indicate
+ * that %r8 should be loaded with -EFAULT to report a userspace
+ * access error.
+ */
+ if (fix->fixup & 1) {
+ regs->gr[8] = -EFAULT;
+ /* zero target register for get_user() */
+ if (parisc_acctyp(0, regs->iir) == VM_READ) {
+ int treg = regs->iir & 0x1f;
+ regs->gr[treg] = 0;
+ }
+ }
regs->iaoq[0] = (unsigned long)&fix->fixup + fix->fixup;
regs->iaoq[0] &= ~3;