Re: [Qemu-devel] Patch to fix mapping of elf pheaders specifying both .data and .bss segments

[Riku Voipio <riku.voipio@iki.fi>]

On Wed, Jun 17, 2009 at 08:36:38PM +0300, Kai Backman wrote:
>    I recently found an issue where an elf pheader mapping both a .data and a
>    .bss segment would have its MemSiz ignored and only FileSiz bytes would
>    end up in the memory map. The bug is exhibiting when an elf interpreter
>    isn't available on the system. I've attached the output of readelf for
>    such a file and a patch against the git repository that fixes the problem.
>    Comments on the patch solicited, I'm also unclear on the commit flow for
>    the project.

I presume you are not using a regular linux userland? A testcase would be nice.
The patch attached is totally messed up thou.

>    diff --git a/linux-user/elfload.c b/linux-user/elfload.c index
>    190ad14..e4e75d5 100644 --- a/linux-user/elfload.c +++
>    b/linux-user/elfload.c @@ -1211,7 +1211,7 @@ int load_elf_binary(struct
>    linux_binprm * bprm, struct target_pt_regs * regs, abi_ulong mapped_addr;
>    struct elf_phdr * elf_ppnt; struct elf_phdr *elf_phdata; - abi_ulong
>    elf_bss, k, elf_brk; + abi_ulong elf_bss, last_bss, mapped_bss, k,
>    elf_brk; int retval; char * elf_interpreter; abi_ulong elf_entry,
>    interp_load_addr = 0; @@ -1271,6 +1271,7 @@ int load_elf_binary(struct
>    linux_binprm * bprm, struct target_pt_regs * regs, elf_ppnt = elf_phdata;
>    elf_bss = 0; + last_bss = 0; elf_brk = 0; @@ -1495,12 +1496,24 @@ int
>    load_elf_binary(struct linux_binprm * bprm, struct target_pt_regs * regs,
>    k = elf_ppnt->p_vaddr + elf_ppnt->p_filesz; if (k > elf_bss) elf_bss = k;
>    + k = elf_ppnt->p_vaddr + elf_ppnt->p_memsz; + if (k > last_bss) +
>    last_bss = k; if ((elf_ppnt->p_flags & PF_X) && end_code < k) end_code =
>    k; if (end_data < k) end_data = k; k = elf_ppnt->p_vaddr +
>    elf_ppnt->p_memsz; if (k > elf_brk) elf_brk = k; + if (!elf_interpreter &&
>    last_bss > elf_bss) { + padzero(elf_bss, last_bss); + mapped_bss =
>    TARGET_ELF_PAGESTART(elf_bss + qemu_host_page_size - 1); + + /* Map the
>    last of the bss segment */ + target_mmap(load_bias + mapped_bss,
>    last_bss-mapped_bss, + PROT_READ|PROT_WRITE|PROT_EXEC, +
>    MAP_FIXED|MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); + } } elf_entry += load_bias;
>    --
>    Kai Backman, Software Engineer, [1]kaib@google.com
> 
> References
> 
>    Visible links
>    1. mailto:kaib@google.com