How to make memory read-only in your C programs.

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How to make memory read-only in your C programs // most of the memory we use in our C programs is readable and writable, but sometimes you want to protect some memory and prevent yourself (or some buggy or malicious code) from changing it. This video shows you how.

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[greg]

Thanks. You always make me think, today you taught me something too. Fifty years coding in C and there is always another trick.

[FreeDomSy-nkue]

I don't think memory protection is part of the C specifications, it's more of an OS thing.
This is also doable in any language that can call OS APIs.
On Windows it's VirtualProtect (or the lower level NtProtectVirtualMemory)

[pablo]

Hi! Im new to C programming and I need to make a program which constantly shows in screen the word that the user types and can be stopped by the key word "END" like this:

Type a word: "hello"

Word is hello

Type a word: "bye"

Word is bye

Type a word: "END"

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It is for a class exercise so it would be amazing if we could use simple functions to make it. Thanks for reading 🙏

[mshingote]

These videos are super high quality content ❤

[starcw]

Great video! Thank you very much Jacob! 🍀

[abdulshabazz]

4:44 Be careful! sysconf returns a 'long' data type which can overflow that declared 'integer' pagesize data type, under certain conditions.

Recommended security patch:

static constexpr long kPageSize = sysconf (_SC_PAGE_SIZE);

Then, if kPageSize fits within the INT_MIN and INT_MAX int data type range, then assign it to the local variable.

[alkaratus]

I remember your lesson about making C code more abstract, we can use this for structures to make their data unchangeable after iniciation. Unless we make special function which will make it possible

[lithiumferrate]

Out of curiosity. Have you ever done windows API programming in C? I've never done so i am curious about how it looks and feels.

[bombrix]

I thought you just make your pointer point to const and it's done 😂

[MatthisDayer]

couldn't you have used aligned_alloc from stdlib? what are the differences?

[mrmfloy]

Just a quick question is there any limitation on branching out else if's (or, similarly, case's on switch) ?
i.e., if (main cond).. else if (cond 1); else if (cond 2); .. else if (cond n). max number of lines/statements, n? Any thoughts? Thanks, .

[Enomem]

If only the compiler had some keyword to help with this...

[mrmfloy]

Great! finally I can make own ram drive. What happens when program exists? Would it be still marked read-only? Say one program initialized ram drive and stayed resident in memory. How could another program access/modify the content of proposed ram drive?

[Jim-vrlx]

Would you recommend this for ephemeral encryption keys? Can the memory page still be swapped out? Is it protected against malicious software in kernel-space; for example, root-kits? POSIX is just an API front-end, right? Is an OS's POSIX sub-system verified by independent groups? Can we ever be sure whats happening to these 'protected' spaces?

[kermitdafrog]

Hmm used malloc but didn't use free.

[duneharv]

So is a segmentation fault always related to a read-only portion of a page in (virtual) memory being written to or are there other causes too?

[rianxFFF]

make videos about binary programming, or more low level programming

[drdca]

9:04 why is p3 6 bytes long while p1 and p2 are 4?
Or are all 3 of them like, 8 bytes long and the leading zeros are just omitted?

[cernejr]

Hmm, in real world code I would want something else than a segfault. I guess one could capture the signal somehow and do some error handling.

[andrewporter]

One thing that no one ever covers though: how do I make memory write-only without having to implement a software solution myself, even if it's cheap? Every cycle counts.