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    Subject[PATCH 2/3] lguest: 2.6.21-mm1 update: lguest-magic-signature.patch
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    Date
    paravirt_probe() and its infrastructure proved as popular as it was
    pretty. In anticipation of its imminent demise, this switches lguest to
    use a magic string to identify a different entry point.

    This is not the long-term solution: that will take a new bootloader rev
    and will hopefully be done in the next few months.

    Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
    ---
    Documentation/lguest/lguest.c | 25 +++++++++++++++++++++----
    drivers/lguest/lguest.c | 2 --
    drivers/lguest/lguest_asm.S | 23 +++++++++--------------
    3 files changed, 30 insertions(+), 20 deletions(-)

    ===================================================================
    --- a/Documentation/lguest/lguest.c
    +++ b/Documentation/lguest/lguest.c
    @@ -96,6 +96,19 @@ static void *map_zeroed_pages(unsigned l
    return (void *)addr;
    }

    +/* Find magic string marking entry point, return entry point. */
    +static unsigned long entry_point(void *start, void *end,
    + unsigned long page_offset)
    +{
    + void *p;
    +
    + for (p = start; p < end; p++)
    + if (memcmp(p, "GenuineLguest", strlen("GenuineLguest")) == 0)
    + return (long)p + strlen("GenuineLguest") + page_offset;
    +
    + err(1, "Is this image a genuine lguest?");
    +}
    +
    /* Returns the entry point */
    static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
    unsigned long *page_offset)
    @@ -103,6 +116,7 @@ static unsigned long map_elf(int elf_fd,
    void *addr;
    Elf32_Phdr phdr[ehdr->e_phnum];
    unsigned int i;
    + unsigned long start = -1UL, end = 0;

    /* Sanity checks. */
    if (ehdr->e_type != ET_EXEC
    @@ -131,6 +145,11 @@ static unsigned long map_elf(int elf_fd,
    *page_offset = phdr[i].p_vaddr - phdr[i].p_paddr;
    else if (*page_offset != phdr[i].p_vaddr - phdr[i].p_paddr)
    errx(1, "Page offset of section %i different", i);
    +
    + if (phdr[i].p_paddr < start)
    + start = phdr[i].p_paddr;
    + if (phdr[i].p_paddr + phdr[i].p_filesz > end)
    + end = phdr[i].p_paddr + phdr[i].p_filesz;

    /* We map everything private, writable. */
    addr = mmap((void *)phdr[i].p_paddr,
    @@ -143,8 +162,7 @@ static unsigned long map_elf(int elf_fd,
    i, addr, (void *)phdr[i].p_paddr);
    }

    - /* Entry is physical address: convert to virtual */
    - return ehdr->e_entry + *page_offset;
    + return entry_point((void *)start, (void *)end, *page_offset);
    }

    /* This is amazingly reliable. */
    @@ -175,8 +193,7 @@ static unsigned long unpack_bzimage(int
    verbose("Unpacked size %i addr %p\n", len, img);
    *page_offset = intuit_page_offset(img, len);

    - /* Entry is physical address: convert to virtual */
    - return (unsigned long)img + *page_offset;
    + return entry_point(img, img + len, *page_offset);
    }

    static unsigned long load_bzimage(int fd, unsigned long *page_offset)
    ===================================================================
    --- a/drivers/lguest/lguest.c
    +++ b/drivers/lguest/lguest.c
    @@ -43,7 +43,6 @@ extern const char lgstart_popf[], lgend_
    extern const char lgstart_popf[], lgend_popf[];
    extern const char lgstart_pushf[], lgend_pushf[];
    extern const char lgstart_iret[], lgend_iret[];
    -extern asmlinkage void lguest_maybe_init(void);
    extern void lguest_iret(void);

    struct lguest_data lguest_data = {
    @@ -497,4 +496,3 @@ __init void lguest_init(void)
    pm_power_off = lguest_power_off;
    start_kernel();
    }
    -paravirt_probe(lguest_maybe_init);
    ===================================================================
    --- a/drivers/lguest/lguest_asm.S
    +++ b/drivers/lguest/lguest_asm.S
    @@ -1,29 +1,24 @@
    #include <linux/linkage.h>
    #include <linux/lguest.h>
    #include <asm/asm-offsets.h>
    +#include <asm/thread_info.h>

    /* FIXME: Once asm/processor-flags.h goes in, include that */
    #define X86_EFLAGS_IF 0x00000200

    /*
    - * This is where we begin: head.S notes that paging is already enabled (which
    - * doesn't happen in native boot) and calls the registered paravirt_probe
    - * functions one at a time. Ours is a simple assembler test for magic
    - * registers. If they're correct we jump to lguest_init.
    + * This is where we begin: we have a magic signature which the launcher looks
    + * for. The plan is that the Linux boot protocol will be extended with a
    + * "platform type" field which will guide us here from the normal entry point,
    + * but for the moment this suffices.
    *
    * We put it in .init.text will be discarded after boot.
    */
    .section .init.text, "ax", @progbits
    -ENTRY(lguest_maybe_init)
    - cmpl $LGUEST_MAGIC_EBP, %ebp
    - jne out
    - cmpl $LGUEST_MAGIC_EDI, %edi
    - jne out
    - cmpl $LGUEST_MAGIC_ESI, %esi
    - jne out
    - je lguest_init
    -out:
    - ret
    +.ascii "GenuineLguest"
    + /* Set up initial stack. */
    + movl $(init_thread_union+THREAD_SIZE),%esp
    + jmp lguest_init

    /* The templates for inline patching. */
    #define LGUEST_PATCH(name, insns...) \

    -
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