Commit e5c460f4 authored May 06, 2014 by David S. Miller

sparc64: Don't bark so loudly about 32-bit tasks generating 64-bit fault addresses.



This was found using Dave Jone's trinity tool.

When a user process which is 32-bit performs a load or a store, the
cpu chops off the top 32-bits of the effective address before
translating it.

This is because we run 32-bit tasks with the PSTATE_AM (address
masking) bit set.

We can't run the kernel with that bit set, so when the kernel accesses
userspace no address masking occurs.

Since a 32-bit process will have no mappings in that region we will
properly fault, so we don't try to handle this using access_ok(),
which can safely just be a NOP on sparc64.

Real faults from 32-bit processes should never generate such addresses
so a bug check was added long ago, and it barks in the logs if this
happens.

But it also barks when a kernel user access causes this condition, and
that _can_ happen.  For example, if a pointer passed into a system call
is "0xfffffffc" and the kernel access 4 bytes offset from that pointer.

Just handle such faults normally via the exception entries.

Signed-off-by: David S. Miller <davem@davemloft.net>

parent 256cf4c4

arch/sparc/mm/fault_64.c

+1 −15

Original line number	Diff line number	Diff line
		@@ -281,18 +281,6 @@ static void noinline __kprobes bogus_32bit_fault_tpc(struct pt_regs *regs)
		show_regs(regs);
		}

		static void noinline __kprobes bogus_32bit_fault_address(struct pt_regs *regs,
		unsigned long addr)
		{
		static int times;

		if (times++ < 10)
		printk(KERN_ERR "FAULT[%s:%d]: 32-bit process "
		"reports 64-bit fault address [%lx]\n",
		current->comm, current->pid, addr);
		show_regs(regs);
		}

		asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
		{
		enum ctx_state prev_state = exception_enter();
		@@ -322,11 +310,9 @@ asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
		goto intr_or_no_mm;
		}
		}
		if (unlikely((address >> 32) != 0)) {
		bogus_32bit_fault_address(regs, address);
		if (unlikely((address >> 32) != 0))
		goto intr_or_no_mm;
		}
		}

		if (regs->tstate & TSTATE_PRIV) {
		unsigned long tpc = regs->tpc;