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Re: access_ok and CONFIG_MIPS32 for 2.6

To: Atsushi Nemoto <anemo@mba.ocn.ne.jp>, ralf@linux-mips.org
Subject: Re: access_ok and CONFIG_MIPS32 for 2.6
From: Dimitri Torfs <dimitri@sonycom.com>
Date: Sun, 4 Jan 2004 22:03:27 +0100
Cc: linux-mips@linux-mips.org
In-reply-to: <20040104.210532.74756709.anemo@mba.ocn.ne.jp>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20040102145941.GA13426@sonycom.com> <20040102194403.GB31092@linux-mips.org> <20040104.210532.74756709.anemo@mba.ocn.ne.jp>
Sender: linux-mips-bounce@linux-mips.org
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On Sun, Jan 04, 2004 at 09:05:32PM +0900, Atsushi Nemoto wrote:
> >>>>> On Fri, 2 Jan 2004 20:44:03 +0100, Ralf Baechle <ralf@linux-mips.org> 
> >>>>> said:
> 
> >> Does anybody know why TASK_SIZE is set to 0x7fff8000 and not
> >> 0x80000000 ?
> 
> ralf> There is a weird special case were 32-bit code running on a
> ralf> 64-bit kernel with c0_status.ux set will behave differently than
> ralf> on a 32-bit processor or with c0_status.ux clear.  The
> ralf> workaround for 64-bit kernels is to leave the top 32kB of the
> ralf> 2GB user virtual address space unused.  For sake of symmetry we
> ralf> do this on both 32-bit and 64-bit kernels.
> 
> Then, access_ok in 2.6 tree is broken, isn't it?
> 
> It seems there should be another definition of USER_DS for
> CONFIG_MIPS32 in 2.6.

Yes, I'm setting USER_DS to 0x80000000 for CONFIG_MIPS32:


--- linux-mips-2.6.orig/include/asm-mips/uaccess.h      2003-11-30 
13:59:06.000000000 +0100
+++ linux.work/include/asm-mips/uaccess.h       2004-01-04 21:22:23.000000000 
+0100
@@ -42,7 +42,12 @@
 #endif /* CONFIG_MIPS64 */
 
 #define KERNEL_DS      ((mm_segment_t) { 0UL })
+
+#ifdef CONFIG_MIPS32
+#define USER_DS                ((mm_segment_t) { 0x80000000UL })
+#else
 #define USER_DS                ((mm_segment_t) { -TASK_SIZE })
+#endif
 
 #define VERIFY_READ    0
 #define VERIFY_WRITE   1


The USER_DS mask is also used in scall32-o32.S, scall64-64.S and
scall64-032.S. It think it would be cleaner if we replace there also
the ">= 0" check with the "== 0" check and add the correct size as you
suggested:


--- linux-mips-2.6.orig/arch/mips/kernel/scall64-64.S   2003-10-11 
00:58:55.000000000 +0200
+++ linux.work/arch/mips/kernel/scall64-64.S    2004-01-04 21:45:45.000000000 
+0100
@@ -119,10 +119,10 @@
        bnez    v0, bad_alignment
 
        LONG_L  v1, TI_ADDR_LIMIT($28)          # in legal address range?
-       LONG_ADDIU      a0, a1, 4
+       LONG_ADDIU      a0, a1, 3 
        or      a0, a0, a1
        and     a0, a0, v1
-       bltz    a0, bad_address
+       bnez    a0, bad_address
 
 #ifdef CONFIG_CPU_HAS_LLSC
        /* Ok, this is the ll/sc case.  World is sane :-)  */


--- linux-mips-2.6.orig/arch/mips/kernel/scall32-o32.S  2003-08-26 
02:28:51.000000000 +0200
+++ linux.work/arch/mips/kernel/scall32-o32.S   2004-01-04 21:48:39.000000000 
+0100
@@ -187,10 +187,10 @@
        bnez    v0, bad_alignment
 
        lw      v1, TI_ADDR_LIMIT($28)          # in legal address range?
-       addiu   a0, a1, 4
+       addiu   a0, a1, 3 
        or      a0, a0, a1
        and     a0, a0, v1
-       bltz    a0, bad_address
+       bnez    a0, bad_address
 
 #ifdef CONFIG_CPU_HAS_LLSC
        /* Ok, this is the ll/sc case.  World is sane :-)  */
@@ -280,11 +280,11 @@
        bnez    v0, sigsegv
 
        addu    v0, t0, 16                      # v0 = usp + 16
-       addu    t1, v0, 12                      # 3 32-bit arguments
+       addu    t1, v0, 11                      # 3 32-bit arguments
        lw      v1, TI_ADDR_LIMIT($28)
        or      v0, v0, t1
        and     v1, v1, v0
-       bltz    v1, efault
+       bnez    v1, efault
 
        move    a0, a1                          # shift argument registers
        move    a1, a2



--- linux-mips-2.6.orig/arch/mips/kernel/scall64-64.S   2003-10-11 
00:58:55.000000000 +0200
+++ linux.work/arch/mips/kernel/scall64-64.S    2004-01-04 21:45:45.000000000 
+0100
@@ -119,10 +119,10 @@
        bnez    v0, bad_alignment
 
        LONG_L  v1, TI_ADDR_LIMIT($28)          # in legal address range?
-       LONG_ADDIU      a0, a1, 4
+       LONG_ADDIU      a0, a1, 3 
        or      a0, a0, a1
        and     a0, a0, v1
-       bltz    a0, bad_address
+       bnez    a0, bad_address
 
 #ifdef CONFIG_CPU_HAS_LLSC
        /* Ok, this is the ll/sc case.  World is sane :-)  */



Dimitri


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