On Thu, Jan 14, 2016 at 12:00 PM, Mike Krinkin <krinkin.m.u@xxxxxxxxx> 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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