Re: [PATCH] (IA64) Fix ugly __[PS]* macros in <asm-ia64/pgtable.h>

From: Jamie Lokier (jamie_at_shareable.org)
Date: 04/15/04

  • Next message: markw_at_osdl.org: "Re: 2.6.5-mm5" 
    Date:	Thu, 15 Apr 2004 16:26:00 +0100
To: davidm@hpl.hp.com

    David Mosberger wrote:
    > >> No, Alpha Linux didn't map data without execute permission.
    >
    > Jamie> That was true from Linux 1.1.67 (when Alpha was introduced)
    > Jamie> to 1.1.84 (when __[PS]* was introduced). I'm not sure the
    > Jamie> Alpha target even worked during those versions. Since Linux
    > Jamie> 1.1.84, it has mapped pages on the Alpha without execute
    > Jamie> permission: the _PAGE_FOE (fault on exec) bit is set for
    > Jamie> mappings which don't have PROT_EXEC.
    >
    > $ uname -a
    > Linux hostname 2.2.20 #2 Wed Mar 20 19:57:28 EST 2002 alpha GNU/Linux
    > $ cat /proc/self/maps | grep cat
    > 0000000120000000-0000000120006000 r-xp 0000000000000000 08:01 309740 /bin/cat
    > 0000000120014000-0000000120016000 rwxp 0000000000004000 08:01 309740 /bin/cat
    >
    > As you can see, the data-segment is mapped with EXEC bit turned on.
    > Ditto for the stack segment, which I think is this one:
    >
    > 000000011fffe000-0000000120000000 rwxp 0000000000000000 00:00 0

    Lest we get more wires crossed, the "x" in /proc/self/maps indicates
    that userspace _requested_ executable mapping with PROT_EXEC.

    It is independent of whether the kernel and hardware can grant a
    non-executable mapping. On my Athlon:

    08048000-0804c000 r-xp 00000000 03:02 95153 /bin/cat
    0804c000-0804d000 rw-p 00003000 03:02 95153 /bin/cat
    bfffe000-c0000000 rwxp fffff000 00:00 0

    The stack is mapped executable, and the data segment is mapped
    non-executable, according to /proc/self/maps which reflects the
    PROT_EXEC request. But in fact because of hardware limitations,
    despite the "rw-p" my data segment is actually executable.

    If you map a segment without PROT_EXEC on Alpha, using a kernel newer
    than 1.1.84, you'll get a non-executable mapping. That's what I mean
    when I say the Alpha maps data without executable permission. The ELF
    loader appears to ask for exec permission anyway, which is another
    thing entirely.

    -- Jamie
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