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Christophe Leroy 89d21e259a powerpc/bpf/32: Fix Oops on tail call tests 
test_bpf tail call tests end up as:

  test_bpf: #0 Tail call leaf jited:1 85 PASS
  test_bpf: #1 Tail call 2 jited:1 111 PASS
  test_bpf: #2 Tail call 3 jited:1 145 PASS
  test_bpf: #3 Tail call 4 jited:1 170 PASS
  test_bpf: #4 Tail call load/store leaf jited:1 190 PASS
  test_bpf: #5 Tail call load/store jited:1
  BUG: Unable to handle kernel data access on write at 0xf1b4e000
  Faulting instruction address: 0xbe86b710
  Oops: Kernel access of bad area, sig: 11 [#1]
  BE PAGE_SIZE=4K MMU=Hash PowerMac
  Modules linked in: test_bpf(+)
  CPU: 0 PID: 97 Comm: insmod Not tainted 6.1.0-rc4+ #195
  Hardware name: PowerMac3,1 750CL 0x87210 PowerMac
  NIP:  be86b710 LR: be857e88 CTR: be86b704
  REGS: f1b4df20 TRAP: 0300   Not tainted  (6.1.0-rc4+)
  MSR:  00009032 <EE,ME,IR,DR,RI>  CR: 28008242  XER: 00000000
  DAR: f1b4e000 DSISR: 42000000
  GPR00: 00000001 f1b4dfe0 c11d2280 00000000 00000000 00000000 00000002 00000000
  GPR08: f1b4e000 be86b704 f1b4e000 00000000 00000000 100d816a f2440000 fe73baa8
  GPR16: f2458000 00000000 c1941ae4 f1fe2248 00000045 c0de0000 f2458030 00000000
  GPR24: 000003e8 0000000f f2458000 f1b4dc90 3e584b46 00000000 f24466a0 c1941a00
  NIP [be86b710] 0xbe86b710
  LR [be857e88] __run_one+0xec/0x264 [test_bpf]
  Call Trace:
  [f1b4dfe0] [00000002] 0x2 (unreliable)
  Instruction dump:
  XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
  XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
  ---[ end trace 0000000000000000 ]---

This is a tentative to write above the stack. The problem is encoutered
with tests added by commit 38608ee7b6 ("bpf, tests: Add load store
test case for tail call")

This happens because tail call is done to a BPF prog with a different
stack_depth. At the time being, the stack is kept as is when the caller
tail calls its callee. But at exit, the callee restores the stack based
on its own properties. Therefore here, at each run, r1 is erroneously
increased by 32 - 16 = 16 bytes.

This was done that way in order to pass the tail call count from caller
to callee through the stack. As powerpc32 doesn't have a red zone in
the stack, it was necessary the maintain the stack as is for the tail
call. But it was not anticipated that the BPF frame size could be
different.

Let's take a new approach. Use register r4 to carry the tail call count
during the tail call, and save it into the stack at function entry if
required. This means the input parameter must be in r3, which is more
correct as it is a 32 bits parameter, then tail call better match with
normal BPF function entry, the down side being that we move that input
parameter back and forth between r3 and r4. That can be optimised later.

Doing that also has the advantage of maximising the common parts between
tail calls and a normal function exit.

With the fix, tail call tests are now successfull:

  test_bpf: #0 Tail call leaf jited:1 53 PASS
  test_bpf: #1 Tail call 2 jited:1 115 PASS
  test_bpf: #2 Tail call 3 jited:1 154 PASS
  test_bpf: #3 Tail call 4 jited:1 165 PASS
  test_bpf: #4 Tail call load/store leaf jited:1 101 PASS
  test_bpf: #5 Tail call load/store jited:1 141 PASS
  test_bpf: #6 Tail call error path, max count reached jited:1 994 PASS
  test_bpf: #7 Tail call count preserved across function calls jited:1 140975 PASS
  test_bpf: #8 Tail call error path, NULL target jited:1 110 PASS
  test_bpf: #9 Tail call error path, index out of range jited:1 69 PASS
  test_bpf: test_tail_calls: Summary: 10 PASSED, 0 FAILED, [10/10 JIT'ed]

Suggested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Fixes: 51c66ad849 ("powerpc/bpf: Implement extended BPF on PPC32")
Cc: stable@vger.kernel.org
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/757acccb7fbfc78efa42dcf3c974b46678198905.1669278887.git.christophe.leroy@csgroup.eu
2022-11-24 23:05:10 +11:00
arch powerpc/bpf/32: Fix Oops on tail call tests 2022-11-24 23:05:10 +11:00
block block-6.1-2022-10-20 2022-10-21 15:14:14 -07:00
certs certs: make system keyring depend on built-in x509 parser 2022-09-24 04:31:18 +09:00
crypto treewide: use get_random_bytes() when possible 2022-10-11 17:42:58 -06:00
Documentation hwmon fixes for v6.1-rc2 2022-10-22 16:04:34 -07:00
drivers Revert "mfd: syscon: Remove repetition of the regmap_get_val_endian()" 2022-10-23 12:04:56 -07:00
fs First batch of EFI fixes for v6.1 2022-10-21 18:02:36 -07:00
include asm-generic: compat: fix compat_arg_u64() and compat_arg_u64_dual() 2022-11-01 10:20:11 +11:00
init init: Kconfig: fix spelling mistake "satify" -> "satisfy" 2022-10-20 21:27:22 -07:00
io_uring io_uring/net: fail zc sendmsg when unsupported by socket 2022-10-22 08:43:03 -06:00
ipc - hfs and hfsplus kmap API modernization from Fabio Francesco 2022-10-12 11:00:22 -07:00
kernel kernel/utsname_sysctl.c: Fix hostname polling 2022-10-23 12:01:01 -07:00
lib Random number generator fixes for Linux 6.1-rc1. 2022-10-16 15:27:07 -07:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm/huge_memory: do not clobber swp_entry_t during THP split 2022-10-20 21:27:24 -07:00
net io_uring-6.1-2022-10-22 2022-10-23 09:55:50 -07:00
rust Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
samples VFIO updates for v6.1-rc1 2022-10-12 14:46:48 -07:00
scripts Kbuild fixes for v6.1 2022-10-16 11:12:22 -07:00
security selinux: enable use of both GFP_KERNEL and GFP_ATOMIC in convert_context() 2022-10-19 09:55:53 -04:00
sound sound fixes for 6.1-rc1 2022-10-14 13:22:14 -07:00
tools RISC-V: 2022-10-23 15:00:43 -07:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt kvm: Add support for arch compat vm ioctls 2022-10-22 05:15:23 -04:00
.clang-format PCI/DOE: Add DOE mailbox support functions 2022-07-19 15:38:04 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
.mailmap mailmap: update email for Qais Yousef 2022-10-20 21:27:21 -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 drm for 5.20/6.0 2022-08-03 19:52:08 -07:00
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 pci-v6.1-fixes-2 2022-10-22 15:52:36 -07:00
Makefile Linux 6.1-rc2 2022-10-23 15:27:33 -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.