I found kernel code that makes system calls. But I thought that was not allowed?2019 Community Moderator ElectionHow can I find the implementations of Linux kernel system calls?Linux Operating system-NOT A KERNEL CHANGE“Modules not found” error during kernel installSystem calls supported in running KernelHow is the linking mechanism so fast in the kernel system calls?Recompile kernel without modules that are not currently in useWhat format is this kernel image? Can not extract kernel code from it?Close file descriptor (in user-space) when UIO driver is unregistered (in kernel)nf_register_hook not found in linux kernel 4.13-rc2 and laterAre system calls part of the kernel or are they part of the OS?
Melting point of aspirin, contradicting sources
How do you respond to a colleague from another team when they're wrongly expecting that you'll help them?
What major Native American tribes were around Santa Fe during the late 1850s?
Could the E-bike drivetrain wear down till needing replacement after 400 km?
Query about absorption line spectra
Can not upgrade Kali,not enough space in /var/cache/apt/archives
Difference between -| and |- in TikZ
Does a 'pending' US visa application constitute a denial?
How is flyblackbird.com operating under Part 91K?
What linear sensor for a keyboard?
anything or something to eat
Have I saved too much for retirement so far?
Is there a name for this algorithm to calculate the concentration of a mixture of two solutions containing the same solute?
Can the Supreme Court overturn an impeachment?
What is the difference between "Do you interest" and "...interested in" something?
How much character growth crosses the line into breaking the character
Flux received by a negative charge
Question about alert, surprise, and crit failing
Python script not running correctly when launched with crontab
Why do IPv6 unique local addresses have to have a /48 prefix?
Engineer refusing to file/disclose patents
Indicating multiple different modes of speech (fantasy language or telepathy)
getting the weights of intermediate layer in keras
Offered money to buy a house, seller is asking for more to cover gap between their listing and mortgage owed
I found kernel code that makes system calls. But I thought that was not allowed?
2019 Community Moderator ElectionHow can I find the implementations of Linux kernel system calls?Linux Operating system-NOT A KERNEL CHANGE“Modules not found” error during kernel installSystem calls supported in running KernelHow is the linking mechanism so fast in the kernel system calls?Recompile kernel without modules that are not currently in useWhat format is this kernel image? Can not extract kernel code from it?Close file descriptor (in user-space) when UIO driver is unregistered (in kernel)nf_register_hook not found in linux kernel 4.13-rc2 and laterAre system calls part of the kernel or are they part of the OS?
Context: linux-5.0/Documentation/process/adding-syscalls.rst#do-not-call-system-calls-in-the-kernel
Firstly, kernel code cannot call functions like "sys_xyzzy()" anymore, because they have the wrong calling convention.
But secondly, "rules on how data may be accessed may differ between kernel data and user data."
There are now some functions which are direct replacements for the old "sys_xyzzy()" calls. For example: ksys_mount().
ksys_mount() takes pointers to __user
memory, just like calls to sys_mount() did. Therefore it should fail if you pass it a pointer to kernel memory. Specifically, it will fail when it calls copy_from_user(), unless you play games with set_fs().
So... why do we have a couple of calls to ksys_mount() in various places inside the kernel? How can these possibly work? They are not wrapped with calls to set_fs().
https://elixir.bootlin.com/linux/v5.0/ident/ksys_mount
- drivers/base/devtmpfs.c
- init/do_mounts.c
- ...
linux-kernel
add a comment |
Context: linux-5.0/Documentation/process/adding-syscalls.rst#do-not-call-system-calls-in-the-kernel
Firstly, kernel code cannot call functions like "sys_xyzzy()" anymore, because they have the wrong calling convention.
But secondly, "rules on how data may be accessed may differ between kernel data and user data."
There are now some functions which are direct replacements for the old "sys_xyzzy()" calls. For example: ksys_mount().
ksys_mount() takes pointers to __user
memory, just like calls to sys_mount() did. Therefore it should fail if you pass it a pointer to kernel memory. Specifically, it will fail when it calls copy_from_user(), unless you play games with set_fs().
So... why do we have a couple of calls to ksys_mount() in various places inside the kernel? How can these possibly work? They are not wrapped with calls to set_fs().
https://elixir.bootlin.com/linux/v5.0/ident/ksys_mount
- drivers/base/devtmpfs.c
- init/do_mounts.c
- ...
linux-kernel
add a comment |
Context: linux-5.0/Documentation/process/adding-syscalls.rst#do-not-call-system-calls-in-the-kernel
Firstly, kernel code cannot call functions like "sys_xyzzy()" anymore, because they have the wrong calling convention.
But secondly, "rules on how data may be accessed may differ between kernel data and user data."
There are now some functions which are direct replacements for the old "sys_xyzzy()" calls. For example: ksys_mount().
ksys_mount() takes pointers to __user
memory, just like calls to sys_mount() did. Therefore it should fail if you pass it a pointer to kernel memory. Specifically, it will fail when it calls copy_from_user(), unless you play games with set_fs().
So... why do we have a couple of calls to ksys_mount() in various places inside the kernel? How can these possibly work? They are not wrapped with calls to set_fs().
https://elixir.bootlin.com/linux/v5.0/ident/ksys_mount
- drivers/base/devtmpfs.c
- init/do_mounts.c
- ...
linux-kernel
Context: linux-5.0/Documentation/process/adding-syscalls.rst#do-not-call-system-calls-in-the-kernel
Firstly, kernel code cannot call functions like "sys_xyzzy()" anymore, because they have the wrong calling convention.
But secondly, "rules on how data may be accessed may differ between kernel data and user data."
There are now some functions which are direct replacements for the old "sys_xyzzy()" calls. For example: ksys_mount().
ksys_mount() takes pointers to __user
memory, just like calls to sys_mount() did. Therefore it should fail if you pass it a pointer to kernel memory. Specifically, it will fail when it calls copy_from_user(), unless you play games with set_fs().
So... why do we have a couple of calls to ksys_mount() in various places inside the kernel? How can these possibly work? They are not wrapped with calls to set_fs().
https://elixir.bootlin.com/linux/v5.0/ident/ksys_mount
- drivers/base/devtmpfs.c
- init/do_mounts.c
- ...
linux-kernel
linux-kernel
edited Mar 15 at 21:24
sourcejedi
asked Mar 13 at 16:32
sourcejedisourcejedi
25.4k445110
25.4k445110
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
devtmpfs
currently runs in a kernel thread. In a kernel thread, addr_limit
is effectively disabled. At least that's how this works for x86 - it is architecture-specific code.
init/do_mounts.c
is similar. The kernel init process must start like a kernel thread, with addr_limit
effectively disabled. Later, it calls do_execve()
to start executing the userspace init program. The kernel makes sure to call "set_fs(USER_DS)", before executing the userspace program.
add a comment |
Your Answer
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "106"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f506120%2fi-found-kernel-code-that-makes-system-calls-but-i-thought-that-was-not-allowed%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
devtmpfs
currently runs in a kernel thread. In a kernel thread, addr_limit
is effectively disabled. At least that's how this works for x86 - it is architecture-specific code.
init/do_mounts.c
is similar. The kernel init process must start like a kernel thread, with addr_limit
effectively disabled. Later, it calls do_execve()
to start executing the userspace init program. The kernel makes sure to call "set_fs(USER_DS)", before executing the userspace program.
add a comment |
devtmpfs
currently runs in a kernel thread. In a kernel thread, addr_limit
is effectively disabled. At least that's how this works for x86 - it is architecture-specific code.
init/do_mounts.c
is similar. The kernel init process must start like a kernel thread, with addr_limit
effectively disabled. Later, it calls do_execve()
to start executing the userspace init program. The kernel makes sure to call "set_fs(USER_DS)", before executing the userspace program.
add a comment |
devtmpfs
currently runs in a kernel thread. In a kernel thread, addr_limit
is effectively disabled. At least that's how this works for x86 - it is architecture-specific code.
init/do_mounts.c
is similar. The kernel init process must start like a kernel thread, with addr_limit
effectively disabled. Later, it calls do_execve()
to start executing the userspace init program. The kernel makes sure to call "set_fs(USER_DS)", before executing the userspace program.
devtmpfs
currently runs in a kernel thread. In a kernel thread, addr_limit
is effectively disabled. At least that's how this works for x86 - it is architecture-specific code.
init/do_mounts.c
is similar. The kernel init process must start like a kernel thread, with addr_limit
effectively disabled. Later, it calls do_execve()
to start executing the userspace init program. The kernel makes sure to call "set_fs(USER_DS)", before executing the userspace program.
edited Mar 13 at 16:37
answered Mar 13 at 16:32
sourcejedisourcejedi
25.4k445110
25.4k445110
add a comment |
add a comment |
Thanks for contributing an answer to Unix & Linux Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f506120%2fi-found-kernel-code-that-makes-system-calls-but-i-thought-that-was-not-allowed%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
-linux-kernel