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Re: [Qemu-devel] Bug#919921: qemu-user Linux ELF loader fails to handle
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [Qemu-devel] Bug#919921: qemu-user Linux ELF loader fails to handle pure BSS segments |
Date: |
Tue, 22 Jan 2019 10:39:25 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 |
Hi Ben,
On 1/22/19 6:43 AM, Michael Tokarev wrote:
> 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) {
This is probably not the good fix, since now your process doesn't have
anything mapped to use his BSS :)
>> + 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 ---
What about this fix instead, using the segment memory size rather than
the file size:
-- >8 --
@@ -2314,7 +2314,7 @@ static void load_elf_image(const char *image_name,
int image_fd,
vaddr = load_bias + eppnt->p_vaddr;
vaddr_po = TARGET_ELF_PAGEOFFSET(vaddr);
vaddr_ps = TARGET_ELF_PAGESTART(vaddr);
- vaddr_len = TARGET_ELF_PAGELENGTH(eppnt->p_filesz + vaddr_po);
+ vaddr_len = TARGET_ELF_PAGELENGTH(eppnt->p_memsz + vaddr_po);
error = target_mmap(vaddr_ps, vaddr_len,
elf_prot, MAP_PRIVATE | MAP_FIXED,
---
>>
>> -- 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
>>
>