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

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)

I absolutely adore this channel.

Great video! Thank you very much Jacob! 🍀

These videos are super high quality content ❤

Thank you!👍👍👍

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

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

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

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.

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.

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

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?

Regarding MAP_ANONYMOUS, I thought process memory was already isolated in Linux? I thought I remembered reading somewhere that malloc was just basically actually handled by mmap and MAP_ANONYMOUS in the kernel space

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

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,.

Can you make brk vs mmap?

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?

What IDE is this?

make videos about binary programming, or more low level programming

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?

Hmm used malloc but didn't use free.

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.

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?

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.

Just had an idea for protecting against "buffer" overrun/underrun, for starters instead of handing the allocation directly to the requester, instead hand over a object that reference the memory by index. The functions for read/write would be similar to the file functions and when handing over the pointer a reference count should be updated in a different page. The allocation itself would always be set to read only when this reference count is greater than 0, serving as a lock against writing. When it's 0 then the protection is removed from the page and the write calls can go ahead without issue. Here's a VERY rough example in code (with some assumed symbols): int main(void) { #define HELLO "Hello World" #define BYE "Goodbye World" /* Ensure we cannot accidentally write more than we need, the 0 indicates we do NOT want this memory to auto grow, the remaining 1s mean pad both the front and back of the memory with null bytes of the size mentioned where sizeof(char) is, this ensures we can always pass the string into any function that expects a null byte */ int strmem = mem_calloc( sizeof(HELLO), 0, sizeof(char), 1, 1 ); /* The 0 indicates that no, the pointer will not be handed to iconv() or some other 3rd party function that does not expect the custom interface */ char *str = NULL; /* This could segfault under different circumstances but on this occasion the count is at 1 so an exclusive lock is possible */ str = memputraw( strmem, STR, sizeof(STR) ); /* This will run without issue as it only reads the memory */ puts( str ); /* This will segfault because the mem_getptr( strmem, true ) was not called */ str[0] = 0; /* Assuming we didn't do the line above then this would start writing "Goodbye World" from position 0 (as indicated by the 0) however only "Goodbye Wor" will actually get written because we specified during allocation we do not want the memory to grow */ str = memputabs( strmem, BYE, sizeof(BYE), 0 ); puts( str ); /* 0 the memory 1st then release it, this will protect against hackers using the pointer after it was released to glean sensitive info */ mem_zero_and_free(strmem); return EXIT_SUCCESS; }

Making memory read-only feels harder than it should be.