linux.git/arch/s390/kernel/vmlinux.lds.S, branch v6.9

s390/boot: simplify GOT handling

2024-02-26T09:25:09+00:00

The end of GOT is calculated dynamically on boot. The size of GOT
is calculated on build from the start and end of GOT. Avoid both
calculations and use the end of GOT directly.

Acked-by: Sumanth Korikkar 
Acked-by: Heiko Carstens 
Signed-off-by: Alexander Gordeev 
Signed-off-by: Heiko Carstens

s390: vmlinux.lds.S: fix .got.plt assertion

2024-02-25T17:01:09+00:00

Naresh reported this build error on linux-next:

s390x-linux-gnu-ld: Unexpected GOT/PLT entries detected!
make[3]: *** [/builds/linux/arch/s390/boot/Makefile:87:
arch/s390/boot/vmlinux.syms] Error 1
make[3]: Target 'arch/s390/boot/bzImage' not remade because of errors.

The reason for the build error is an incorrect/incomplete assertion which
checks the size of the .got.plt section. Similar to x86 the size is either
zero or 24 bytes (three entries).

See commit 262b5cae67a6 ("x86/boot/compressed: Move .got.plt entries out of
the .got section") for more details. The three reserved/additional entries
for s390 are described in chapter 3.2.2 of the s390x ABI [1] (thanks to
Andreas Krebbel for pointing this out!).

[1] https://github.com/IBM/s390x-abi/releases/download/v1.6.1/lzsabi_s390x.pdf

Reported-by: Naresh Kamboju 
Reported-by: Linux Kernel Functional Testing 
Closes: https://lore.kernel.org/all/CA+G9fYvWp8TY-fMEvc3UhoVtoR_eM5VsfHj3+n+kexcfJJ+Cvw@mail.gmail.com
Fixes: 30226853d6ec ("s390: vmlinux.lds.S: explicitly handle '.got' and '.plt' sections")
Signed-off-by: Heiko Carstens

s390: compile relocatable kernel without -fPIE

2024-02-20T13:37:33+00:00

On s390, currently kernel uses the '-fPIE' compiler flag for compiling
vmlinux.  This has a few problems:

  - It uses dynamic symbols (.dynsym), for which the linker refuses to
    allow more than 64k sections.  This can break features which use
    '-ffunction-sections' and '-fdata-sections', including kpatch-build
    [1] and Function Granular KASLR.

  - It unnecessarily uses GOT relocations, adding an extra layer of
    indirection for many memory accesses.

Instead of using '-fPIE', resolve all the relocations at link time and
then manually adjust any absolute relocations (R_390_64) during boot.

This is done by first telling the linker to preserve all relocations
during the vmlinux link.  (Note this is harmless: they are later
stripped in the vmlinux.bin link.)

Then use the 'relocs' tool to find all absolute relocations (R_390_64)
which apply to allocatable sections.  The offsets of those relocations
are saved in a special section which is then used to adjust the
relocations during boot.

(Note: For some reason, Clang occasionally creates a GOT reference, even
without '-fPIE'.  So Clang-compiled kernels have a GOT, which needs to
be adjusted.)

On my mostly-defconfig kernel, this reduces kernel text size by ~1.3%.

[1] https://github.com/dynup/kpatch/issues/1284
[2] https://gcc.gnu.org/pipermail/gcc-patches/2023-June/622872.html
[3] https://gcc.gnu.org/pipermail/gcc-patches/2023-August/625986.html

Compiler consideration:

Gcc recently implemented an optimization [2] for loading symbols without
explicit alignment, aligning with the IBM Z ELF ABI. This ABI mandates
symbols to reside on a 2-byte boundary, enabling the use of the larl
instruction. However, kernel linker scripts may still generate unaligned
symbols. To address this, a new -munaligned-symbols option has been
introduced [3] in recent gcc versions. This option has to be used with
future gcc versions.

Older Clang lacks support for handling unaligned symbols generated
by kernel linker scripts when the kernel is built without -fPIE. However,
future versions of Clang will include support for the -munaligned-symbols
option. When the support is unavailable, compile the kernel with -fPIE
to maintain the existing behavior.

In addition to it:
move vmlinux.relocs to safe relocation

When the kernel is built with CONFIG_KERNEL_UNCOMPRESSED, the entire
uncompressed vmlinux.bin is positioned in the bzImage decompressor
image at the default kernel LMA of 0x100000, enabling it to be executed
in-place. However, the size of .vmlinux.relocs could be large enough to
cause an overlap with the uncompressed kernel at the address 0x100000.
To address this issue, .vmlinux.relocs is positioned after the
.rodata.compressed in the bzImage. Nevertheless, in this configuration,
vmlinux.relocs will overlap with the .bss section of vmlinux.bin. To
overcome that, move vmlinux.relocs to a safe location before clearing
.bss and handling relocs.

Compile warning fix from Sumanth Korikkar:

When kernel is built with CONFIG_LD_ORPHAN_WARN and -fno-PIE, there are
several warnings:

ld: warning: orphan section `.rela.iplt' from
`arch/s390/kernel/head64.o' being placed in section `.rela.dyn'
ld: warning: orphan section `.rela.head.text' from
`arch/s390/kernel/head64.o' being placed in section `.rela.dyn'
ld: warning: orphan section `.rela.init.text' from
`arch/s390/kernel/head64.o' being placed in section `.rela.dyn'
ld: warning: orphan section `.rela.rodata.cst8' from
`arch/s390/kernel/head64.o' being placed in section `.rela.dyn'

Orphan sections are sections that exist in an object file but don't have
a corresponding output section in the final executable. ld raises a
warning when it identifies such sections.

Eliminate the warning by placing all .rela orphan sections in .rela.dyn
and raise an error when size of .rela.dyn is greater than zero. i.e.
Dont just neglect orphan sections.

This is similar to adjustment performed in x86, where kernel is built
with -fno-PIE.
commit 5354e84598f2 ("x86/build: Add asserts for unwanted sections")

[sumanthk@linux.ibm.com: rebased Josh Poimboeuf patches and move
 vmlinux.relocs to safe location]
[hca@linux.ibm.com: merged compile warning fix from Sumanth]
Tested-by: Sumanth Korikkar 
Acked-by: Vasily Gorbik 
Signed-off-by: Josh Poimboeuf 
Signed-off-by: Sumanth Korikkar 
Link: https://lore.kernel.org/r/20240219132734.22881-4-sumanthk@linux.ibm.com
Link: https://lore.kernel.org/r/20240219132734.22881-5-sumanthk@linux.ibm.com
Signed-off-by: Heiko Carstens

s390: vmlinux.lds.S: explicitly keep various sections

2024-02-14T12:50:52+00:00

When building with CONFIG_LD_ORPHAN_WARN after selecting
CONFIG_ARCH_HAS_LD_ORPHAN_WARN, there are some warnings around certain
ELF sections:

  s390-linux-ld: warning: orphan section `.dynstr' from `arch/s390/kernel/head64.o' being placed in section `.dynstr'
  s390-linux-ld: warning: orphan section `.dynamic' from `arch/s390/kernel/head64.o' being placed in section `.dynamic'
  s390-linux-ld: warning: orphan section `.hash' from `arch/s390/kernel/head64.o' being placed in section `.hash'
  s390-linux-ld: warning: orphan section `.gnu.hash' from `arch/s390/kernel/head64.o' being placed in section `.gnu.hash'

Explicitly keep those sections like other architectures when
CONFIG_RELOCATABLE is enabled, which is always true for s390.

[hca@linux.ibm.com: keep sections instead of discarding]
Signed-off-by: Nathan Chancellor 
Link: https://lore.kernel.org/r/20240207-s390-lld-and-orphan-warn-v1-4-8a665b3346ab@kernel.org
Signed-off-by: Heiko Carstens

s390: vmlinux.lds.S: explicitly handle '.got' and '.plt' sections

2024-02-14T12:50:52+00:00

When building with CONFIG_LD_ORPHAN_WARN after selecting
CONFIG_ARCH_HAS_LD_ORPHAN_WARN, there are a lot of warnings around the
GOT and PLT sections:

  s390-linux-ld: warning: orphan section `.plt' from `arch/s390/kernel/head64.o' being placed in section `.plt'
  s390-linux-ld: warning: orphan section `.got' from `arch/s390/kernel/head64.o' being placed in section `.got'
  s390-linux-ld: warning: orphan section `.got.plt' from `arch/s390/kernel/head64.o' being placed in section `.got.plt'
  s390-linux-ld: warning: orphan section `.iplt' from `arch/s390/kernel/head64.o' being placed in section `.iplt'
  s390-linux-ld: warning: orphan section `.igot.plt' from `arch/s390/kernel/head64.o' being placed in section `.igot.plt'

  s390-linux-ld: warning: orphan section `.iplt' from `arch/s390/boot/head.o' being placed in section `.iplt'
  s390-linux-ld: warning: orphan section `.igot.plt' from `arch/s390/boot/head.o' being placed in section `.igot.plt'
  s390-linux-ld: warning: orphan section `.got' from `arch/s390/boot/head.o' being placed in section `.got'

Currently, only the '.got' section is actually emitted in the final
binary. In a manner similar to other architectures, put the '.got'
section near the '.data' section and coalesce the PLT sections,
checking that the final section is zero sized, which is a safe/tested
approach versus full discard.

Signed-off-by: Nathan Chancellor 
Tested-by: Justin Stitt 
Link: https://lore.kernel.org/r/20240207-s390-lld-and-orphan-warn-v1-3-8a665b3346ab@kernel.org
Signed-off-by: Heiko Carstens

s390: vmlinux.lds.S: handle '.data.rel' sections explicitly

2024-02-14T12:50:52+00:00

When building with CONFIG_LD_ORPHAN_WARN after selecting
CONFIG_ARCH_HAS_LD_ORPHAN_WARN, there are a lot of warnings around
'.data.rel' sections:

  s390-linux-ld: warning: orphan section `.data.rel' from `kernel/sched/build_utility.o' being placed in section `.data.rel'
  s390-linux-ld: warning: orphan section `.data.rel.local' from `kernel/sched/build_utility.o' being placed in section `.data.rel.local'
  s390-linux-ld: warning: orphan section `.data.rel.ro' from `kernel/sched/build_utility.o' being placed in section `.data.rel.ro'
  s390-linux-ld: warning: orphan section `.data.rel.ro.local' from `kernel/sched/build_utility.o' being placed in section `.data.rel.ro.local'

Describe these in vmlinux.lds.S so there is no more warning and the
sections are placed consistently between linkers.

Signed-off-by: Nathan Chancellor 
Tested-by: Justin Stitt 
Link: https://lore.kernel.org/r/20240207-s390-lld-and-orphan-warn-v1-2-8a665b3346ab@kernel.org
Signed-off-by: Heiko Carstens

s390/fpu: get rid of test_fp_ctl()

2023-12-11T13:33:06+00:00

It is quite subtle to use test_fp_ctl() correctly. Therefore remove it -
instead copy whatever new floating point control (fpc) register values are
supposed to be used into its save area.

Test the validity of the new value when loading it. If the new value is
invalid, load the fpc register with zero.

This seems to be a the best way to approach this problem. Even though this
changes behavior:

- sigreturn with an invalid fpc value on the stack will succeed, and
  continue with zero value, instead of returning with SIGSEGV

- ptraced processes will also use a zero value instead of letting the
  request fail with -EINVAL

However all of this seems to acceptable. After all testing of the value was
only implemented to avoid that user space can crash the kernel. It is not
there to test values for validity; and the assumption is that there is no
existing user space which is doing this.

Reviewed-by: Claudio Imbrenda 
Signed-off-by: Heiko Carstens 
Signed-off-by: Alexander Gordeev

s390: make extables read-only

2023-04-04T16:34:55+00:00

Currently, exception tables are marked as ro_after_init. However,
since they are sorted during compile time using scripts/sorttable,
they can be moved to RO_DATA using the RO_EXCEPTION_TABLE_ALIGN macro,
which is specifically designed for this purpose.

Suggested-by: Heiko Carstens 
Reviewed-by: Heiko Carstens 
Signed-off-by: Vasily Gorbik

s390/kasan: move shadow mapping to decompressor

2023-03-20T10:02:51+00:00

Since regular paging structs are initialized in decompressor already
move KASAN shadow mapping to decompressor as well. This helps to avoid
allocating KASAN required memory in 1 large chunk, de-duplicate paging
structs creation code and start the uncompressed kernel with KASAN
instrumentation right away. This also allows to avoid all pitfalls
accidentally calling KASAN instrumented code during KASAN initialization.

Acked-by: Heiko Carstens 
Reviewed-by: Alexander Gordeev 
Signed-off-by: Vasily Gorbik 
Signed-off-by: Heiko Carstens

Merge tag 's390-6.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux

2023-02-21T23:09:17+00:00

Pull s390 updates from Heiko Carstens:

 - Large cleanup of the con3270/tty3270 driver. Among others this fixes:
     - Background Color Support
     - ASCII Line Character Support
     - VT100 Support
     - Geometries other than 80x24

 - Cleanup and improve cmpxchg() code. Also add cmpxchg_user_key() to
   uaccess functions, which will be used by KVM to access KVM guest
   memory with a specific storage key

 - Add support for user space events counting to CPUMF

 - Cleanup the vfio/ccw code, which also allows now to properly support
   2K Format-2 IDALs

 - Move kernel page table allocation and initialization to decompressor,
   which finally allows to enter the kernel with dynamic address
   translation enabled. This in turn allows to get rid of code with
   special handling in the kernel, which has to distinguish if DAT is on
   or off

 - Replace kretprobe with rethook

 - Various improvements to vfio/ap queue resets:
     - Use TAPQ to verify completion of a reset in progress rather than
       multiple invocations of ZAPQ.
     - Check TAPQ response codes when verifying successful completion of
       ZAPQ.
     - Fix erroneous handling of some error response codes.
     - Increase the maximum amount of time to wait for successful
       completion of ZAPQ

 - Rework system call wrappers to get rid of alias functions, which were
   only left on s390

 - Cleanup diag288_wdt watchdog driver. It has been agreed on with
   Guenter Roeck that this goes upstream via the s390 tree

 - Add missing loadparm parameter handling for list-directed ECKD
   ipl/reipl

 - Various improvements to memory detection code

 - Remove arch_cpu_idle_time() since the current implementation is
   broken, and allows user space observable accounted idle times which
   can temporarily decrease

 - Add Reset DAT-Protection support: (only) allow to change PTEs from RO
   to RW with a new RDP instruction. Unlike the currently used IPTE
   instruction, this does not necessarily guarantee that TLBs of all
   CPUs are synchronously flushed; and that remote CPUs can see spurious
   protection faults. The overall improvement for not requiring an all
   CPU synchronization, like it is required with IPTE, should be
   beneficial

 - Fix KFENCE page fault reporting

 - Smaller cleanups and improvement all over the place

* tag 's390-6.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux: (182 commits)
  s390/irq,idle: simplify idle check
  s390/processor: add test_and_set_cpu_flag() and test_and_clear_cpu_flag()
  s390/processor: let cpu helper functions return boolean values
  s390/kfence: fix page fault reporting
  s390/zcrypt: introduce ctfm field in struct CPRBX
  s390: remove confusing comment from uapi types header file
  vfio/ccw: remove WARN_ON during shutdown
  s390/entry: remove toolchain dependent micro-optimization
  s390/mem_detect: do not truncate online memory ranges info
  s390/vx: remove __uint128_t type from __vector128 struct again
  s390/mm: add support for RDP (Reset DAT-Protection)
  s390/mm: define private VM_FAULT_* reasons from top bits
  Documentation: s390: correct spelling
  s390/ap: fix status returned by ap_qact()
  s390/ap: fix status returned by ap_aqic()
  s390: vfio-ap: tighten the NIB validity check
  Revert "s390/mem_detect: do not update output parameters on failure"
  s390/idle: remove arch_cpu_idle_time() and corresponding code
  s390/vx: use simple assignments to access __vector128 members
  s390/vx: add 64 and 128 bit members to __vector128 struct
  ...