Is there a way to proactively avoid segfault?

Question

Here's the situation:

I analyze the interaction of programs with the driver using the LD_PRELOADed module, which intercepts the ioctl () system call. The system I'm working with (Linux kernel 2.6.18), fortunately, has the length of the data encoded in the query parameter, so I can happily dump ioctl data with the right length.

However, many of this data has pointers to other structures, and I do not know their length (this is what I study in the end). Therefore, I look at the data for pointers and dump the data to this position. I am worried that this may leave my code open for segfaults if the pointer is close to the segment boundary (and my early testing seems to show that it is).

So, I was wondering what I can do to preempt whether the current process checks for a specific bias before trying to dereference? Is it possible?

Edit: just an update, since I forgot to mention something that can be very important, the target system is based on MIPS, although I am also testing my module on my x86 machine.

Answer 1

/dev/null write(null_fd, ptr, size). -1 errno, EFAULT, . size, . / POSIX, .

Answer 2

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Answer 3

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Answer 4

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If so, the page borders are well-limited (either 4K or 8K), so a simple address masking should deal with it.