I am apologizing for sending again. I have forgotten to add all recipients to previous e-mail. ...

-------- Forwarded Message -------- Subject: Re: mmap 0-th page Date: Fri, 9 Aug 2024 12:45:01 +0200 From: michal.hrachovec@volny.cz michal.hrachovec@volny.cz To: Jiri Slaby jirislaby@kernel.org

Good afternoon,

I finally have in Fedora Linux kernel version 6.10.3: Linux fedora 6.10.3-100.fc39.x86_64 #1 SMP PREEMPT_DYNAMIC Mon Aug  5 14:46:47 UTC 2024 x86_64 GNU/Linux

I have set this setting to zero: cat /proc/sys/vm/mmap_min_addr 0

Then I compiled your program, where I only added the main and the return statements:

int main(void) { char *zero = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0); *(char *)(NULL) = 'A'; printf("%c\n", *zero); return 0; }

I got error at running the compiled program: Program received signal SIGSEGV, Segmentation fault (at line 2 of your program)

Can you help again, please.

Thank you.

Michal Hrachovec

On 7/31/24 09:43, Jiri Slaby wrote:

On 31. 07. 24, 9:39, Jiri Slaby wrote:

...

On 26. 07. 24, 12:36, michal.hrachovec@volny.cz wrote:

...

I am trying to allocate the 0-th page with mmap function in my code. I am always getting this error with this error-code: mmap error ffffffff Then I was searching the internet for this topic and I have found the same topic at stackoverflow web pages.

char *zero = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);          *(char *)(NULL) = 'A';          printf("%c\n", *zero);

still yields 'A' here with 6.10.2 w/ vm.mmap_min_addr=0.

Yeah and mind LSMs...