Doesn't allowing a user mode program to access kernel space memory and execute the IN and OUT instructions defeat the purpose of having CPU modes?Questions on Linux kernel internalsHigh memory (user space) and highmem (kernel space)What mode of memory at the time linux kernel was loaded?How is user space process/thread controlled by the operating systemGet quota usage information as non-privileged userRewrite a system call in userspaceWhere are “the kernel stack”, “Frames for C run-time startup functions”, and “Frame for main()” in the memory layout of a program?What's the use of having a kernel part in the virtual memory space of Linux processes?Linux Kernel Mode Vs User ModeCan a device driver that accesses an IO device directly run in user mode?
What will happen if my luggage gets delayed?
Windows Server Data Center Edition - Unlimited Virtual Machines
Specifying a starting column with colortbl package and xcolor
This Alpine town?
In the late 1940’s to early 1950’s what technology was available that could melt ice?
Are small insurances worth it?
NASA's RS-25 Engines
What is the population of Romulus in the TNG era?
Would an aboleth's Phantasmal Force lair action be affected by Counterspell, Dispel Magic, and/or Slow?
What is the generally accepted pronunciation of “topoi”?
Why does cron require MTA for logging?
I reported the illegal activity of my boss to his boss. My boss found out. Now I am being punished. What should I do?
How do we create new idioms and use them in a novel?
Damage bonus for different weapons
Power Strip for Europe
Vocabulary for giving just numbers, not a full answer
Why do we say ‘pairwise disjoint’, rather than ‘disjoint’?
Signed and unsigned numbers
Outlet with 3 sets of wires
What is Tony Stark injecting into himself in Iron Man 3?
Getting the || sign while using Kurier
Can one live in the U.S. and not use a credit card?
Has a sovereign Communist government ever run, and conceded loss, on a fair election?
Why restrict private health insurance?
Doesn't allowing a user mode program to access kernel space memory and execute the IN and OUT instructions defeat the purpose of having CPU modes?
Questions on Linux kernel internalsHigh memory (user space) and highmem (kernel space)What mode of memory at the time linux kernel was loaded?How is user space process/thread controlled by the operating systemGet quota usage information as non-privileged userRewrite a system call in userspaceWhere are “the kernel stack”, “Frames for C run-time startup functions”, and “Frame for main()” in the memory layout of a program?What's the use of having a kernel part in the virtual memory space of Linux processes?Linux Kernel Mode Vs User ModeCan a device driver that accesses an IO device directly run in user mode?
When the CPU is in user mode, the CPU can't execute privileged instructions and can't access kernel space memory.
And when the CPU is in kernel mode, the CPU can execute all instructions and can access all memory.
Now in Linux, a user mode program can access all memory (using /dev/mem) and can execute the two privileged instructions IN and OUT (using iopl() I think).
So a user mode program in Linux can do most things (I think most things) that can be done in kernel mode.
Doesn't allowing a user mode program to have all this power defeats the purpose of having CPU modes?
linux
edited 3 hours ago
ilkkachu
60.7k1098172
asked 4 hours ago
user341099user341099
61
New contributor
user341099 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
When the CPU is in user mode, the CPU can't execute privileged instructions and can't access kernel space memory.
And when the CPU is in kernel mode, the CPU can execute all instructions and can access all memory.
Now in Linux, a user mode program can access all memory (using /dev/mem) and can execute the two privileged instructions IN and OUT (using iopl() I think).
So a user mode program in Linux can do most things (I think most things) that can be done in kernel mode.
Doesn't allowing a user mode program to have all this power defeats the purpose of having CPU modes?
linux
edited 3 hours ago
ilkkachu
60.7k1098172
asked 4 hours ago
user341099user341099
61
New contributor
user341099 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
When the CPU is in user mode, the CPU can't execute privileged instructions and can't access kernel space memory.
And when the CPU is in kernel mode, the CPU can execute all instructions and can access all memory.
Now in Linux, a user mode program can access all memory (using /dev/mem) and can execute the two privileged instructions IN and OUT (using iopl() I think).
So a user mode program in Linux can do most things (I think most things) that can be done in kernel mode.
Doesn't allowing a user mode program to have all this power defeats the purpose of having CPU modes?
linux
edited 3 hours ago
ilkkachu
60.7k1098172
asked 4 hours ago
user341099user341099
61
New contributor
user341099 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
When the CPU is in user mode, the CPU can't execute privileged instructions and can't access kernel space memory.
And when the CPU is in kernel mode, the CPU can execute all instructions and can access all memory.
Now in Linux, a user mode program can access all memory (using /dev/mem) and can execute the two privileged instructions IN and OUT (using iopl() I think).
So a user mode program in Linux can do most things (I think most things) that can be done in kernel mode.
Doesn't allowing a user mode program to have all this power defeats the purpose of having CPU modes?
linux
linux
edited 3 hours ago
ilkkachu
60.7k1098172
asked 4 hours ago
user341099user341099
61
New contributor
user341099 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 3 hours ago
ilkkachu
60.7k1098172
asked 4 hours ago
user341099user341099
61
New contributor
user341099 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 3 hours ago
ilkkachu
60.7k1098172
edited 3 hours ago
ilkkachu
60.7k1098172
edited 3 hours ago
ilkkachu
60.7k1098172
60.7k1098172
asked 4 hours ago
user341099user341099
61
New contributor
user341099 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 4 hours ago
user341099user341099
61
asked 4 hours ago
user341099user341099
61
61
New contributor
user341099 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
user341099 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
user341099 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
So a user mode program in Linux can do most things (I think most things) that can be done in kernel mode.
Well, not all use mode programs can, only those with the appropriate privileges. And that's determined by the kernel.
/dev/mem is protected by the usual filesystem access permissions, and the CAP_SYS_RAWIO capability. iopl() and ioperm() are also restricted through the same capability.
/dev/mem can also be compiled out of the kernel altogether (CONFIG_DEVMEM).
Doesn't allowing a user mode program to have all this power defeats the purpose of having CPU modes?
Well, maybe. It depends on what you want privileged user-space processes to be able to do. User-space processes can also trash the whole hard drive if they have access to /dev/sda (or equivalent), even though that defeats the purpose of having a filesystem driver to handle storage access.
(Then there's also the fact that iopl() works by utilizing the CPU privilege modes on i386, so it can't well be said to defeat their purpose.)
edited 3 hours ago
Stephen Kitt
175k24400477
answered 3 hours ago
ilkkachuilkkachu
60.7k1098172
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
);
);
user341099 is a new contributor. Be nice, and check out our Code of Conduct.
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%2f505527%2fdoesnt-allowing-a-user-mode-program-to-access-kernel-space-memory-and-execute-t%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
So a user mode program in Linux can do most things (I think most things) that can be done in kernel mode.
Well, not all use mode programs can, only those with the appropriate privileges. And that's determined by the kernel.
/dev/mem is protected by the usual filesystem access permissions, and the CAP_SYS_RAWIO capability. iopl() and ioperm() are also restricted through the same capability.
/dev/mem can also be compiled out of the kernel altogether (CONFIG_DEVMEM).
Doesn't allowing a user mode program to have all this power defeats the purpose of having CPU modes?
Well, maybe. It depends on what you want privileged user-space processes to be able to do. User-space processes can also trash the whole hard drive if they have access to /dev/sda (or equivalent), even though that defeats the purpose of having a filesystem driver to handle storage access.
(Then there's also the fact that iopl() works by utilizing the CPU privilege modes on i386, so it can't well be said to defeat their purpose.)
edited 3 hours ago
Stephen Kitt
175k24400477
answered 3 hours ago
ilkkachuilkkachu
60.7k1098172
add a comment |
So a user mode program in Linux can do most things (I think most things) that can be done in kernel mode.
Well, not all use mode programs can, only those with the appropriate privileges. And that's determined by the kernel.
/dev/mem is protected by the usual filesystem access permissions, and the CAP_SYS_RAWIO capability. iopl() and ioperm() are also restricted through the same capability.
/dev/mem can also be compiled out of the kernel altogether (CONFIG_DEVMEM).
Doesn't allowing a user mode program to have all this power defeats the purpose of having CPU modes?
Well, maybe. It depends on what you want privileged user-space processes to be able to do. User-space processes can also trash the whole hard drive if they have access to /dev/sda (or equivalent), even though that defeats the purpose of having a filesystem driver to handle storage access.
(Then there's also the fact that iopl() works by utilizing the CPU privilege modes on i386, so it can't well be said to defeat their purpose.)
edited 3 hours ago
Stephen Kitt
175k24400477
answered 3 hours ago
ilkkachuilkkachu
60.7k1098172
add a comment |
So a user mode program in Linux can do most things (I think most things) that can be done in kernel mode.
Well, not all use mode programs can, only those with the appropriate privileges. And that's determined by the kernel.
/dev/mem is protected by the usual filesystem access permissions, and the CAP_SYS_RAWIO capability. iopl() and ioperm() are also restricted through the same capability.
/dev/mem can also be compiled out of the kernel altogether (CONFIG_DEVMEM).
Doesn't allowing a user mode program to have all this power defeats the purpose of having CPU modes?
Well, maybe. It depends on what you want privileged user-space processes to be able to do. User-space processes can also trash the whole hard drive if they have access to /dev/sda (or equivalent), even though that defeats the purpose of having a filesystem driver to handle storage access.
(Then there's also the fact that iopl() works by utilizing the CPU privilege modes on i386, so it can't well be said to defeat their purpose.)
edited 3 hours ago
Stephen Kitt
175k24400477
answered 3 hours ago
ilkkachuilkkachu
60.7k1098172
So a user mode program in Linux can do most things (I think most things) that can be done in kernel mode.
Well, not all use mode programs can, only those with the appropriate privileges. And that's determined by the kernel.
/dev/mem is protected by the usual filesystem access permissions, and the CAP_SYS_RAWIO capability. iopl() and ioperm() are also restricted through the same capability.
/dev/mem can also be compiled out of the kernel altogether (CONFIG_DEVMEM).
Doesn't allowing a user mode program to have all this power defeats the purpose of having CPU modes?
Well, maybe. It depends on what you want privileged user-space processes to be able to do. User-space processes can also trash the whole hard drive if they have access to /dev/sda (or equivalent), even though that defeats the purpose of having a filesystem driver to handle storage access.
(Then there's also the fact that iopl() works by utilizing the CPU privilege modes on i386, so it can't well be said to defeat their purpose.)
edited 3 hours ago
Stephen Kitt
175k24400477
answered 3 hours ago
ilkkachuilkkachu
60.7k1098172
edited 3 hours ago
Stephen Kitt
175k24400477
edited 3 hours ago
Stephen Kitt
175k24400477
edited 3 hours ago
Stephen Kitt
175k24400477
175k24400477
answered 3 hours ago
ilkkachuilkkachu
60.7k1098172
answered 3 hours ago
ilkkachuilkkachu
60.7k1098172
answered 3 hours ago
ilkkachuilkkachu
60.7k1098172
60.7k1098172
add a comment |
add a comment |
user341099 is a new contributor. Be nice, and check out our Code of Conduct.
user341099 is a new contributor. Be nice, and check out our Code of Conduct.
user341099 is a new contributor. Be nice, and check out our Code of Conduct.
user341099 is a new contributor. Be nice, and check out our Code of Conduct.
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%2f505527%2fdoesnt-allowing-a-user-mode-program-to-access-kernel-space-memory-and-execute-t%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
