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Michael Ellerman d45c4b48da powerpc: Hide empty pt_regs at base of the stack 
A thread started via eg. user_mode_thread() runs in the kernel to begin
with and then may later return to userspace. While it's running in the
kernel it has a pt_regs at the base of its kernel stack, but that
pt_regs is all zeroes.

If the thread oopses in that state, it leads to an ugly stack trace with
a big block of zero GPRs, as reported by Joel:

  Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc7-00004-gf7757129e3de-dirty #3
  Hardware name: IBM PowerNV (emulated by qemu) POWER9 0x4e1200 opal:v7.0 PowerNV
  Call Trace:
  [c0000000036afb00] [c0000000010dd058] dump_stack_lvl+0x6c/0x9c (unreliable)
  [c0000000036afb30] [c00000000013c524] panic+0x178/0x424
  [c0000000036afbd0] [c000000002005100] mount_root_generic+0x250/0x324
  [c0000000036afca0] [c0000000020057d0] prepare_namespace+0x2d4/0x344
  [c0000000036afd20] [c0000000020049c0] kernel_init_freeable+0x358/0x3ac
  [c0000000036afdf0] [c0000000000111b0] kernel_init+0x30/0x1a0
  [c0000000036afe50] [c00000000000debc] ret_from_kernel_user_thread+0x14/0x1c
  --- interrupt: 0 at 0x0
  NIP:  0000000000000000 LR: 0000000000000000 CTR: 0000000000000000
  REGS: c0000000036afe80 TRAP: 0000   Not tainted  (6.5.0-rc7-00004-gf7757129e3de-dirty)
  MSR:  0000000000000000 <>  CR: 00000000  XER: 00000000
  CFAR: 0000000000000000 IRQMASK: 0
  GPR00: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR04: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR08: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR12: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR24: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  GPR28: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  NIP [0000000000000000] 0x0
  LR [0000000000000000] 0x0
  --- interrupt: 0

The all-zero pt_regs looks ugly and conveys no useful information, other
than its presence. So detect that case and just show the presence of the
frame by printing the interrupt marker, eg:

  Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc3-00126-g18e9506562a0-dirty #301
  Hardware name: IBM pSeries (emulated by qemu) POWER9 (raw) 0x4e1202 0xf000005 of:SLOF,HEAD hv:linux,kvm pSeries
  Call Trace:
  [c000000003aabb00] [c000000001143db8] dump_stack_lvl+0x6c/0x9c (unreliable)
  [c000000003aabb30] [c00000000014c624] panic+0x178/0x424
  [c000000003aabbd0] [c0000000020050fc] mount_root_generic+0x250/0x324
  [c000000003aabca0] [c0000000020057cc] prepare_namespace+0x2d4/0x344
  [c000000003aabd20] [c0000000020049bc] kernel_init_freeable+0x358/0x3ac
  [c000000003aabdf0] [c0000000000111b0] kernel_init+0x30/0x1a0
  [c000000003aabe50] [c00000000000debc] ret_from_kernel_user_thread+0x14/0x1c
  --- interrupt: 0 at 0x0

To avoid ever suppressing a valid pt_regs make sure the pt_regs has a
zero MSR and TRAP value, and is located at the very base of the stack.

Fixes: 6895dfc047 ("powerpc: copy_thread fill in interrupt frame marker and back chain")
Reported-by: Joel Stanley <joel@jms.id.au>
Reported-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230824064210.907266-1-mpe@ellerman.id.au
2023-10-19 21:38:29 +11:00
arch powerpc: Hide empty pt_regs at base of the stack 2023-10-19 21:38:29 +11:00
block blk-mq: fix tags UAF when shrinking q->nr_hw_queues 2023-09-11 16:17:34 -06:00
certs certs: Reference revocation list for all keyrings 2023-08-17 20:12:41 +00:00
crypto This update includes the following changes: 2023-08-29 11:23:29 -07:00
Documentation Driver core fix for 6.6-rc2 2023-09-16 11:26:52 -07:00
drivers macintosh/macio-adb: add missing iounmap() on error in macio_init() 2023-10-19 17:16:20 +11:00
fs stat: remove no-longer-used helper macros 2023-09-17 10:46:12 -07:00
include vmcore: remove dependency with is_kdump_kernel() for exporting vmcore 2023-09-18 12:23:27 +10:00
init workqueue: Changes for v6.6 2023-09-01 16:06:32 -07:00
io_uring io_uring/net: fix iter retargeting for selected buf 2023-09-14 10:12:55 -06:00
ipc Add x86 shadow stack support 2023-08-31 12:20:12 -07:00
kernel Fix a performance regression on large SMT systems, an Intel SMT4 2023-09-17 11:10:23 -07:00
lib powerpc: Use shared font data 2023-10-01 23:09:02 +11:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm vm: fix move_vma() memory accounting being off 2023-09-16 15:23:31 -07:00
net kcm: Fix error handling for SOCK_DGRAM in kcm_sendmsg(). 2023-09-14 10:43:51 +02:00
rust Documentation work keeps chugging along; stuff for 6.6 includes: 2023-08-30 20:05:42 -07:00
samples VFIO updates for v6.6-rc1 2023-08-30 20:36:01 -07:00
scripts Kbuild fixes for v6.6 2023-09-16 15:27:00 -07:00
security selinux: fix handling of empty opts in selinux_fs_context_submount() 2023-09-12 17:31:08 -04:00
sound sound fixes for 6.6-rc1 2023-09-08 13:07:50 -07:00
tools selftests/powerpc: Fix emit_tests to work with run_kselftest.sh 2023-09-22 20:29:48 +10:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
virt ARM: 2023-09-07 13:52:20 -07:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: rpm-pkg: rename binkernel.spec to kernel.spec 2023-07-25 00:59:33 +09:00
.mailmap for-linus-2023083101 2023-09-01 12:31:44 -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 USB: Remove Wireless USB and UWB documentation 2023-08-09 14:17:32 +02:00
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 This pull-request renames the genpd subsystem to pmdomain. 2023-09-13 14:18:19 -07:00
Makefile Linux 6.6-rc2 2023-09-17 14:40:24 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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 Restructured Text 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.