[3.11.y.z extended stable] Patch "sparc64: Don't bark so loudly about 32-bit tasks generating 64-bit fault addresses." has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From cc27cd2a02c0a23e81ae5cfcf3cc92dba8c69b71 Mon Sep 17 00:00:00 2001
From: "David S. Miller" <davem at davemloft.net>
Date: Tue, 6 May 2014 21:27:37 -0700
Subject: sparc64: Don't bark so loudly about 32-bit tasks generating 64-bit
 fault addresses.

commit e5c460f46ae7ee94831cb55cb980f942aa9e5a85 upstream.

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 at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/sparc/mm/fault_64.c | 16 +---------------
 1 file changed, 1 insertion(+), 15 deletions(-)

diff --git a/arch/sparc/mm/fault_64.c b/arch/sparc/mm/fault_64.c
index 1992fa04095f..ea83f82464da 100644
--- a/arch/sparc/mm/fault_64.c
+++ b/arch/sparc/mm/fault_64.c
@@ -280,18 +280,6 @@ 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)
 {
 	struct mm_struct *mm = current->mm;
@@ -320,10 +308,8 @@ 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) {
--
1.9.1