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Jens Remus cea5589e95 s390/boot: Do not adjust GOT entries for undef weak sym 
Since commit 778666df60 ("s390: compile relocatable kernel without
-fPIE") and commit 00cda11d3b ("s390: Compile kernel with -fPIC and
link with -no-pie") the kernel on s390x may have a Global Offset Table
(GOT) whose entries are adjusted for KASLR in kaslr_adjust_got().

The GOT may contain entries for undefined weak symbols that resolved to
zero. That is the resulting GOT entry value is zero. Adjusting those
entries unconditionally in kaslr_adjust_got() is wrong. Otherwise the
following sample code would erroneously assume foo to be defined, due to
the adjustment changing the zero-value to a non-zero one:

  extern int foo __attribute__((weak));
  if (*foo)
    /* foo is defined [or undefined and erroneously adjusted] */

The vmlinux build at commit 00cda11d3b ("s390: Compile kernel with
-fPIC and link with -no-pie") with defconfig actually had two GOT
entries for the undefined weak symbols __start_BTF and __stop_BTF:

$ objdump -tw vmlinux | grep -F "*UND*"
0000000000000000  w      *UND*  0000000000000000 __stop_BTF
0000000000000000  w      *UND*  0000000000000000 __start_BTF

$ readelf -rw vmlinux | grep -E "R_390_GOTENT +0{16}"
000000345760  2776a0000001a R_390_GOTENT      0000000000000000 __stop_BTF + 2
000000345766  2d5480000001a R_390_GOTENT      0000000000000000 __start_BTF + 2

The s390-specific vmlinux linker script sets the section start to
__START_KERNEL, which is currently defined as 0x100000 on s390x. Access
to lowcore is performed via a pointer of 0 and not a symbol in a section
starting at 0. The first 64K are reserved for the loader on s390x. Thus
it is safe to assume that __START_KERNEL will never be 0. As a result
there cannot be any defined symbols resolving to zero in the kernel.

Note that the first three GOT entries are reserved for the dynamic
loader on s390x. [1] In the kernel they are zero. Therefore no extra
handling is required to skip these.

Skip adjusting GOT entries with a value of zero in kaslr_adjust_got().

While at it update the comment when a GOT exists on s390x. Since commit
00cda11d3b ("s390: Compile kernel with -fPIC and link with -no-pie")
it no longer only exists when compiling with Clang, but also with GCC.

[1]: s390x ELF ABI, section "Global Offset Table",
     https://github.com/IBM/s390x-abi/releases

Fixes: 778666df60 ("s390: compile relocatable kernel without -fPIE")
Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>
Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
2024-06-25 14:39:42 +02:00
arch s390/boot: Do not adjust GOT entries for undef weak sym 2024-06-25 14:39:42 +02:00
block blk-throttle: Fix incorrect display of io.max 2024-05-30 19:44:29 -06:00
certs kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
crypto This push fixes a bug in the new ecc P521 code as well as a buggy 2024-05-20 08:47:54 -07:00
Documentation dma-mapping fixes for Linux 6.10 2024-05-31 12:14:55 -07:00
drivers s390/sclp: Fix sclp_init() cleanup on failure 2024-06-24 11:07:06 +02:00
fs 2 small smb3 fixes 2024-06-01 14:35:57 -07:00
include TTY fix for 6.10-rc2 2024-06-01 08:53:39 -07:00
init Driver core changes for 6.10-rc1 2024-05-22 12:13:40 -07:00
io_uring io_uring/net: assign kmsg inq/flags before buffer selection 2024-05-30 14:04:37 -06:00
ipc Mainly singleton patches, documented in their respective changelogs. 2024-05-19 14:02:03 -07:00
kernel Kbuild fixes for v6.10 2024-06-01 09:33:55 -07:00
lib kunit/fortify: Remove __kmalloc_node() test 2024-05-31 13:47:41 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm 16 hotfixes, 11 of which are cc:stable. 2024-05-25 15:10:33 -07:00
net Including fixes from bpf and netfilter. 2024-05-30 08:33:04 -07:00
rust LoongArch changes for v6.10 2024-05-22 09:43:07 -07:00
samples tracing/treewide: Remove second parameter of __assign_str() 2024-05-22 20:14:47 -04:00
scripts dt-bindings: kbuild: Fix dt_binding_check on unconfigured build 2024-05-30 01:15:58 +09:00
security landlock: Fix d_parent walk 2024-05-31 16:41:52 +02:00
sound ALSA: seq: ump: Fix swapped song position pointer data 2024-05-31 09:51:44 +02:00
tools KVM: s390x: selftests: Add shared zeropage test 2024-06-05 17:03:24 +02:00
usr kbuild: use $(src) instead of $(srctree)/$(src) for source directory 2024-05-10 04:34:52 +09:00
virt The usual shower of singleton fixes and minor series all over MM, 2024-05-19 09:21:03 -07:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig
.editorconfig Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: create a list of all built DTB files 2024-02-19 18:20:39 +09:00
.mailmap mailmap: update entry for Kees Cook 2024-05-31 08:58:36 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Drop Gustavo Pimentel as PCI DWC Maintainer 2024-03-27 13:41:02 -05:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS sound fixes for 6.10-rc2 2024-05-31 12:11:44 -07:00
Makefile Linux 6.10-rc2 2024-06-02 15:44:56 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.