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105 Commits

Author SHA1 Message Date
linD026
1a6fb67cf2
Fix potential concurrent access problems with VFS (#108) 
Since Linux v3.14, the read, write and seek operations of "struct file" are
guaranteed for thread safety [1][2]. This patch added an explanation.

Here are the potential problems:
chardev.c:
- Move the "msg_ptr" pointer into the read function to remove unnecessary usage.
- List the clear states of "already_open" by using mnemonic enumeration.

chardev2.c:
- The "buffer" in the write function is user space data. It cannot use in the
  kernel space.
- Reduce the redundant type transformation.
- List the states of "already_open". Same as chardev.c.

[1] https://lore.kernel.org/lkml/20140303210359.26624.qmail@science.horizon.com/T/#u
[2] 9c225f2655
 2021-09-23 12:20:10 +08:00
Jim Huang
027f39c0c1 Denote LWN hyperlink 2021-09-23 00:36:42 +08:00
Ylowy
24257e837e
Typo. 2021-09-19 20:39:56 +08:00
Stacy Prowell
728b7fd432
Fixed parameter name for hello-5. 
Parameters are case-sensitive, so myintArray is different from myintarray, and people who are running the example with copy/paste will find it doesn't work as described in the text.
 2021-09-15 16:05:26 -04:00
Gilad Reti
e8d5bf7fd4
fix typo: compatibiity -> compatibility 2021-09-12 08:54:53 +03:00
Jim Huang
c519f57403 Simplify the wording 2021-09-10 14:19:22 +00:00
linD026
62dbb1b7b8
Adapt the timer API Usage (#98) 
Since v4.14 [1], the timer API has been changed to improve memory safety.
The series of improvements ended up at v4.15 [2].

Reference: https://lwn.net/Articles/735887/

Close #97

[1] 686fef928b
[2] 841b86f328
 2021-09-10 12:29:48 +08:00
linD026
148fb013ee
Avoid unexpected concurrent access (#94) 
In file {chardev,chardev2,sleep}.c, the variable to determine
the exclusive access was of integer type, which led to race
condition.

This patch rewrote the above with atomic CAS respectively
to eliminate the race.

Close #93
 2021-09-07 23:42:06 +08:00
ccs100203
56c99328b3 Fix Typo 
from "mask" to "masks"
from "quick" to "quickly"
from "a" to "an"
 2021-09-03 23:02:17 +08:00
Jim Huang
6110f8ee3c Rewrite the descriptions about bottom half 2021-09-01 12:07:25 +08:00
linzhien
5cd96a80c9 Fix typo 2021-09-01 07:44:40 +08:00
linD026
cccc98ab2c
Fix disallowed cr0 write protection and close_fd (#80) 
Since the commit 8dbec27a242cd3e2816eeb98d3237b9f57cf6232 [1]
(kernel version v5.3+ [2]) the sensitive CR0 bits in x86 is pinned,
we need to use the inline asm [3][4] to bypass it.

commit 8dbec27a242cd3e2816eeb98d3237b9f57cf6232 :
> With sensitive CR4 bits pinned now, it's possible that the WP bit for
> CR0 might become a target as well.
>
> Following the same reasoning for the CR4 pinning, pin CR0's WP
> bit. Contrary to the cpu feature dependend CR4 pinning this can be done
> with a constant value.

Also, getting "sys_call_table" [8] from the symbol lookup by using the address
of "close_fd" does not work for v5.11+ [5][6]. The reason is the entry of
"sys_call_table[__NR_close]" is not the address of "close_fd", actually
it is "__x64_sys_close" in x86.

Two solutions were proposed: using "kallsyms_lookup_name" [7] or just specifying
the address into the module. The symbol "kallsyms_lookup_name"  is unexported
since v5.7; the address of "sys_call_table" can be found in
"/boot/System.map" or "/proc/kallsyms".

Since v5.7, the manual symbol lookup is not guaranteed to work
because of control-flow integrity (or control-flow enforcement [9][10]) is added
[11] for x86, but it is disabled since v5.11 [12][13]. To make sure manual symbol
lookup work, it only uses up to v5.4.

Reference:
[1] 8dbec27a24
[2] https://outflux.net/blog/archives/2019/11/14/security-things-in-linux-v5-3/
[3] https://patchwork.kernel.org/project/linux-kbuild/patch/20200903203053.3411268-3-samitolvanen@google.com/
[4] https://stackoverflow.com/questions/58512430/how-to-write-to-protected-pages-in-the-linux-kernel
[5] https://lore.kernel.org/bpf/20201120231441.29911-21-ebiederm@xmission.com/
[6] https://lore.kernel.org/bpf/87blj83ysq.fsf@x220.int.ebiederm.org/
[7] 0bd476e6c6
[8] 8f27766a88
[9] https://lore.kernel.org/lkml/20200204171425.28073-1-yu-cheng.yu@intel.com/
[10] https://lore.kernel.org/linux-doc/20201110162211.9207-1-yu-cheng.yu@intel.com/T/
[11] 5790921bc1
[12] 20bf2b3787
[13] https://lore.kernel.org/bpf/20210128123842.c9e33949e62f504b84bfadf5@gmail.com/
 2021-08-31 11:07:01 +08:00
xatier
1f9f201940
Update Archlinux kernel headers instructions 
`linux-libre-headers` has been moved to AUR [1]. We can simply install `linux-headers` [2] instead.

[1] https://aur.archlinux.org/packages/linux-libre-headers/
[2] https://archlinux.org/packages/core/x86_64/linux-headers/
 2021-08-25 20:11:27 -07:00
Jim Huang
ecfe9606de Get rid of the initial 0 that shows up in every (sub)section 
Every section and subsection number can be eliminated by adding the
renewcommand.

Suggested by Lars Engebretsen.
 2021-08-24 19:02:16 +08:00
Brad Baker
8012508508 Fixing typo 2021-08-24 00:15:47 -04:00
fennecJ
870b26fa2d Update several example code for newer kernel 
Known issues with current example code:
If you using newer kernel(e.g linux 5.11.x) to compile the example code,
you may meet following error:
1. syscall.c:83:50: error: ‘ksys_close’ undeclared;
2. cryptosk.c:17:24: error: field ‘sg’ has incomplete type
3. cryptosk.c:143:9: error: implicit declaration of function
‘get_random_bytes’
4. error: macro "DECLARE_TASKLET" passed 3 arguments, but takes just 2

Solutions/workaround:
1. In syscall.c, replace #include <linux/syscalls.h> with
#include <linux/fdtable.h> and replace  ksys_close with close_fd
if the kernel version >= 5.11. [1][2]
2. Add #include <linux/scatterlist.h> into cryptosk.c
3. Add #include <linux/random.h> into cryptosk.c
4. In bottomhalf.c and example_tasklet.c, replace DECLARE_TASKLET
with DECLARE_TASKLET_OLD and dispose third argument(0L). [3]

[1] - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1572bfdf21d4d50e51941498ffe0b56c2289f783
[2] - https://www.mail-archive.com/meta-arago@arago-project.org//msg11939.html
[3] - https://patchwork.kernel.org/project/kernel-hardening/patch/20200716030847.1564131-3-keescook@chromium.org/
 2021-08-23 21:30:43 +08:00
Jim Huang
22e50f3ce9 Use recent kernel build messages 2021-08-20 01:05:51 +08:00
Jim Huang
f7e2186e6b Revise the version magic descriptions for recent kernels 2021-08-20 01:02:20 +08:00
Jim Huang
3c742b0c7c Fix wording 2021-08-20 00:29:43 +08:00
Cyril Brulebois
98aa78e4d2 Adjust link to ioctl-number.rst 2021-08-16 21:54:03 +02:00
Cyril Brulebois
c43c01db31 Improve wording (avoid a send/sent repetition along the way) 2021-08-16 21:54:03 +02:00
Cyril Brulebois
08b6de2cde Use an https:// link for LWN 2021-08-16 21:54:03 +02:00
Cyril Brulebois
8861d1ead7 Improve wording (statistics seem gathered, not stat-ed) 2021-08-16 21:54:03 +02:00
Cyril Brulebois
4d5649fc08 Improve wording (there's only one kernel) 2021-08-16 21:54:03 +02:00
Cyril Brulebois
3e05439b6d Add emphasis for the y/m values 2021-08-16 21:54:03 +02:00
Cyril Brulebois
b5ab7c5e88 Fix various typos 2021-08-16 21:54:03 +02:00
fennecJ
467cc83cc7
Improve the descriptions about reference count (#62) 
The term "reference count" would be better than "use count."
In addition, the usage of module_refcount(THIS_MODULE) was appended
for the reference counter query.
 2021-08-17 00:23:22 +08:00
fennecj
99faf5ed0f Fix typo 2021-08-16 23:48:04 +08:00
Jim Huang
4acc65b740 Use \verb for the identifiers starting with "--" 2021-08-16 21:21:10 +08:00
Chih-Yu Chen
c8238430b2
Avoid incorrectly separated words (#55) 
This patch fixed some typos and added the missing punctuation.
 2021-08-16 18:45:43 +08:00
fennecj
15e44bffa8 Fix grammar and typo 2021-08-16 00:47:23 +08:00
Jim Huang
964f14dda6 Annotate more directories/files 2021-08-13 01:02:21 +08:00
fennecj
990358d75a Fix typo 2021-08-13 00:52:33 +08:00
fennecj
b656755300 Fix typo 2021-08-11 18:34:23 +08:00
Jim Huang
8d7caa7fc9 Make insmod/rmmod more consistent 2021-08-11 15:08:08 +08:00
fennecj
e87998c224 Fix incorrect path 
There should be a space between uname and -r
 2021-08-10 18:22:33 +08:00
Jim Huang
6b6083fca2 Remove out-of-date information 2021-08-09 23:59:59 +08:00
Jim Huang
b002e43bb8 Annotate NULL 2021-08-09 23:57:30 +08:00
Jim Huang
e800505b8f Point to corresponding kernel header 2021-08-09 23:26:01 +08:00
Jim Huang
a4c44ed3d1 Annotate more commands 2021-08-09 23:23:08 +08:00
Jim Huang
2d368210ce Introduce \src to generate Linux kernel source hyperlinks 
The new command \src was introduced for preliminary hyperlink generation
which points to Linux kernel source code. At present, stable/linux.git
was referred:
  https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git

We might switch to specific LTS kernels once requested.
 2021-08-09 23:01:34 +08:00
Jim Huang
da3dd34cd2 Revise the path of Linux kernel headers 
This patch uses the relative path to Linux kernel headers in source tree
rather than what they are usually inclused in LKM. It would be great to
introduce \href with appropriate hyperlinks to Linux kernel tree.
 2021-08-09 22:37:20 +08:00
Jim Huang
e551c98dde Clarify kernel header inclusion 
Both <linux/module.h> and <linux/kernel.h> are essential headers, and
LKM should include them. Here, we do not use the fully qualified path
specifying the headers.
 2021-08-09 22:05:08 +08:00
Jim Huang
251adeb075 Change the header file which defines sys_delete_module 2021-08-09 22:00:57 +08:00
Jim Huang
526ad3c842 Annotate function calls 2021-08-09 21:41:50 +08:00
Jim Huang
53ef0614e8 Annotate more commands 2021-08-09 21:35:19 +08:00
Jim Huang
971148e3ed Annotate 'mknod' command 2021-08-09 21:19:40 +08:00
Jim Huang
2ac8a81945 Add hyperlinks to microkernel examples 2021-08-09 21:17:22 +08:00
Jim Huang
5786975d89 Update tLDP hyperlink 2021-08-09 21:12:04 +08:00
Jim Huang
bb3466461a Add hyperlink to Understanding The Linux Kernel 2021-08-09 21:11:15 +08:00