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[PATCH] mips_atomic_set fixups (with LLSC)

Subject: [PATCH] mips_atomic_set fixups (with LLSC)
From: Liam Davies <>
Date: Thu, 06 Dec 2001 15:43:54 +1000
Organization: AgileTV Corporation
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.6) Gecko/20011120

The kernel can be caused to crash when making the following syscall
sysmips(MIPS_ATOMIC_SET, [unaligned addr], value, 0);

The latest mips_atomic_set does not use the fixups that are defined
for the ll/sc instructions.

If an unaligned address is passed in we take the exception and
unaligned.c:emulate_load_store_insn ignores the fixups for the
ll/sc and sends a SIGBUS instead, thus causing the kernel to die.

The patch is to make the ll/sc instructions lookup the fixup table
and do them if present.

Also the fixup for the instructions in scall_o32.S appears to be
inappropriate, so the fixup is set to be bad_addr and an -EFAULT
is returned from the syscall.


Liam Davies

--- ../sgi-cvs/arch/mips/kernel/unaligned.c     Mon Dec  3 10:49:23 2001
+++ arch/mips/kernel/unaligned.c        Thu Dec  6 15:07:00 2001
@@ -114,12 +114,14 @@
         * These are instructions that a compiler doesn't generate.  We
         * can assume therefore that the code is MIPS-aware and
         * really buggy.  Emulating these instructions would break the
-        * semantics anyway.
+        * semantics anyway. However, we do want to look at the exception
+        * table to see if we can exit gracefully.
        case ll_op:
        case lld_op:
        case sc_op:
        case scd_op:
+               goto fault;
         * For these instructions the only way to create an address
--- ../sgi-cvs/arch/mips/kernel/scall_o32.S     Mon Oct  8 09:56:02 2001
+++ arch/mips/kernel/scall_o32.S        Thu Dec  6 15:34:47 2001
@@ -201,7 +201,7 @@
        or      a0, a0, a1
        li      v0, -EFAULT
        and     a0, a0, v1
-       bltz    a0, 8f
+       bltz    a0, bad_address
        /* Ok, this is the ll/sc case.  World is sane :-)  */
@@ -211,8 +211,8 @@
        beqz    a0, 1b
        .section __ex_table,"a"
-       PTR     1b, bad_stack
-       PTR     2b, bad_stack
+       PTR     1b, bad_address
+       PTR     2b, bad_address
        sw      a1, 16(sp)
@@ -256,8 +256,9 @@
 no_mem:        li      v0, -ENOMEM
        jr      ra
-8:     li      v0, -EFAULT
-9:     jr      ra
+       li      v0, -EFAULT
+       jr      ra

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