lkml.org 
[lkml]   [2012]   [Jun]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[ 07/69] powerpc: Fix kernel panic during kernel module load
    3.2-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Steffen Rumler <steffen.rumler.ext@nsn.com>

    commit 3c75296562f43e6fbc6cddd3de948a7b3e4e9bcf upstream.

    This fixes a problem which can causes kernel oopses while loading
    a kernel module.

    According to the PowerPC EABI specification, GPR r11 is assigned
    the dedicated function to point to the previous stack frame.
    In the powerpc-specific kernel module loader, do_plt_call()
    (in arch/powerpc/kernel/module_32.c), GPR r11 is also used
    to generate trampoline code.

    This combination crashes the kernel, in the case where the compiler
    chooses to use a helper function for saving GPRs on entry, and the
    module loader has placed the .init.text section far away from the
    .text section, meaning that it has to generate a trampoline for
    functions in the .init.text section to call the GPR save helper.
    Because the trampoline trashes r11, references to the stack frame
    using r11 can cause an oops.

    The fix just uses GPR r12 instead of GPR r11 for generating the
    trampoline code. According to the statements from Freescale, this is
    safe from an EABI perspective.

    I've tested the fix for kernel 2.6.33 on MPC8541.

    Signed-off-by: Steffen Rumler <steffen.rumler.ext@nsn.com>
    [paulus@samba.org: reworded the description]
    Signed-off-by: Paul Mackerras <paulus@samba.org>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    arch/powerpc/kernel/module_32.c | 11 +++++------
    1 file changed, 5 insertions(+), 6 deletions(-)

    diff --git a/arch/powerpc/kernel/module_32.c b/arch/powerpc/kernel/module_32.c
    index 0b6d796..2e3200c 100644
    --- a/arch/powerpc/kernel/module_32.c
    +++ b/arch/powerpc/kernel/module_32.c
    @@ -176,8 +176,8 @@ int module_frob_arch_sections(Elf32_Ehdr *hdr,

    static inline int entry_matches(struct ppc_plt_entry *entry, Elf32_Addr val)
    {
    - if (entry->jump[0] == 0x3d600000 + ((val + 0x8000) >> 16)
    - && entry->jump[1] == 0x396b0000 + (val & 0xffff))
    + if (entry->jump[0] == 0x3d800000 + ((val + 0x8000) >> 16)
    + && entry->jump[1] == 0x398c0000 + (val & 0xffff))
    return 1;
    return 0;
    }
    @@ -204,10 +204,9 @@ static uint32_t do_plt_call(void *location,
    entry++;
    }

    - /* Stolen from Paul Mackerras as well... */
    - entry->jump[0] = 0x3d600000+((val+0x8000)>>16); /* lis r11,sym@ha */
    - entry->jump[1] = 0x396b0000 + (val&0xffff); /* addi r11,r11,sym@l*/
    - entry->jump[2] = 0x7d6903a6; /* mtctr r11 */
    + entry->jump[0] = 0x3d800000+((val+0x8000)>>16); /* lis r12,sym@ha */
    + entry->jump[1] = 0x398c0000 + (val&0xffff); /* addi r12,r12,sym@l*/
    + entry->jump[2] = 0x7d8903a6; /* mtctr r12 */
    entry->jump[3] = 0x4e800420; /* bctr */

    DEBUGP("Initialized plt for 0x%x at %p\n", val, entry);



    \
     
     \ /
      Last update: 2012-06-17 21:01    [W:4.057 / U:0.028 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site