Re: [Qemu-devel] Bug#919921: qemu-user Linux ELF loader fails to handle pure BSS segments

[Michael Tokarev <mjt@tls.msk.ru>]

Forwarding to qemu-devel@
http://bugs.debian.org/919921

Thanks!

20.01.2019 20:55, Ben Hutchings wrote:
> Package: qemu-user
> Version: 1:3.1+dfsg-2
> Severity: normal
> Tags: patch
> 
> I've been building and testing klibc across many architectures using
> qemu-user, and I found that qemu-user fails to load a few programs on
> a few architectures, reporting an EINVAL error code.  Here's the
> "readelf -l" output for one such program:
> 
>      Elf file type is EXEC (Executable file)
>      Entry point 0x10000100
>      There are 5 program headers, starting at offset 52
>      
>      Program Headers:
>        Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
>        PHDR           0x000034 0x10000034 0x10000034 0x000a0 0x000a0 R   0x4
>        INTERP         0x0000d4 0x100000d4 0x100000d4 0x0002a 0x0002a R   0x1
>            [Requesting program interpreter: /lib/klibc-R7FVdnsTBUFpWPgCV6FR07b-mf8.so]
>        LOAD           0x000000 0x10000000 0x10000000 0x002f8 0x002f8 R E 0x10000
>        LOAD           0x010000 0x10020000 0x10020000 0x00000 0x08000 RW  0x10000
>        GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RWE 0x10
>      
>       Section to Segment mapping:
>        Segment Sections...
>         00
>         01     .interp
>         02     .interp .text .rodata .eh_frame
>         03     .bss
>         04
> 
> The unusual feature of this program, and all the others that failed,
> is that there is a LOAD segment with a file-size of 0 (i.e.  only BSS,
> no initialised data).  load_elf_image() will try to mmap() initialised
> data for this section even though there is none and a length of 0 is
> invalid.
> 
> The change that seems to fix this is to skip the mmap() in this case:
> 
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -2316,11 +2316,13 @@ static void load_elf_image(const char *i
>               vaddr_ps = TARGET_ELF_PAGESTART(vaddr);
>               vaddr_len = TARGET_ELF_PAGELENGTH(eppnt->p_filesz + vaddr_po);
>   
> -            error = target_mmap(vaddr_ps, vaddr_len,
> -                                elf_prot, MAP_PRIVATE | MAP_FIXED,
> -                                image_fd, eppnt->p_offset - vaddr_po);
> -            if (error == -1) {
> -                goto exit_perror;
> +            if (vaddr_len != 0) {
> +                error = target_mmap(vaddr_ps, vaddr_len,
> +                                    elf_prot, MAP_PRIVATE | MAP_FIXED,
> +                                    image_fd, eppnt->p_offset - vaddr_po);
> +                if (error == -1) {
> +                    goto exit_perror;
> +                }
>               }
>   
>               vaddr_ef = vaddr + eppnt->p_filesz;
> --- END ---
> 
> -- System Information:
> Debian Release: buster/sid
>    APT prefers unstable-debug
>    APT policy: (500, 'unstable-debug'), (500, 'stable-updates'), (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental')
> Architecture: amd64 (x86_64)
> Foreign Architectures: i386
> 
> Kernel: Linux 4.19.0-1-amd64 (SMP w/4 CPU cores)
> Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB.UTF-8 (charmap=UTF-8)
> Shell: /bin/sh linked to /bin/dash
> Init: systemd (via /run/systemd/system)
> LSM: AppArmor: enabled
> 
> Versions of packages qemu-user depends on:
> ii  libc6         2.28-3
> ii  libcapstone3  3.0.5-3
> ii  libgcc1       1:8.2.0-13
> ii  libglib2.0-0  2.58.1-2
> ii  libstdc++6    8.2.0-13
> ii  zlib1g        1:1.2.11.dfsg-1
> 
> Versions of packages qemu-user recommends:
> ii  qemu-user-static [qemu-user-binfmt]  1:3.1+dfsg-2
> 
> Versions of packages qemu-user suggests:
> ii  sudo  1.8.26-2
> 
> -- no debconf information
>