On Thu, Jan 14, 2016 at 12:00 PM, Mike Krinkin <krinkin.m.u@gmail.com> wrote:
Hi, i have a couple of questions to clarify, if you don't mind
On Thu, Jan 14, 2016 at 11:04:28AM -0500, Kenneth Adam Miller wrote:
I have a custom drive and userland program pair that I'm using for a very special use case at my workplace where we are mapping specific physical address ranges into userland memory with a mmap callback. Everything works together well with a C userland program that calls into our driver's ioctl and mmap definitions, but for our case we are using an alternative systems language just for the userland program.
So you have userland app written in C, and another not written in C? The former works well while the latter doesn't, am i right?
Yes, the former works in so much as mmap completes successfully. I've verified that the parameters are identical in the non-C program. The issue of just using the C only program is that the actual implementation of interest is in the non-C program, and that's because that language facilitates other features that are *required* on our end.
That mmap call is failing (properly as we want) out from the driver's mmap implementation due to the fact that the vm_flags have the VM_EXEC flag set. We do not want users to be able to map the memory range as executable, so the driver should check for this as it does. The issue is in the fact that somewhere between where mmap is called and when the parameters are given to the driver, the vma->vm_flags are being set to 255. I've manually checked the values being given to the mmap call in our non-C binary, and they are *equivalent* in value to that of the C program.
By "manually" do you mean strace? Could you show strace output for both apps? And also could you show readelf -l output for both binaries?
By manually, I mean with a print call just before the mmap call in each of the programs. Right now, I'm working on getting a strace output, but I have to run that in qemu. To be able to run it in qemu in order to isolate the driver and all from my host, I have to build with buildroot. So I'll email that when I get it, but it'll be a while.
My question is, is there anything that can cause the vma->vm_flags to be changed in the trip between when the user land program calls mmap and
when
control is delivered to the mmap callback?
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