Messages in this thread | | | Date | Thu, 31 Jul 2014 11:46:53 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] ARM/ARM64: don't enter kgdb when userspace executes a kgdb break instruction. |
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On Thu, Jul 31, 2014 at 06:33:23AM +0100, Omar Sandoval wrote: > Hi,
Hi Omar,
> On Wed, Jul 30, 2014 at 12:24:14PM +0100, Will Deacon wrote: > > Whilst this sounds like a worrying problem, I've failed to reproduce it > > on arm64. Executing a brk instruction with either KGDB_DYN_DGB_BRK_IMM or > > KDBG_COMPILED_DBG_BRK_IMM immediates from userspace results in a SIGTRAP being > > delivered, assumedly because kgdb_handle_exception simply returns when kgdb > > isn't active. > > From what I can tell, the break hooks are registered so long as kgdb is enabled > at all - i.e., the kernel was compiled with CONFIG_KGDB=y and, for example, > CONFIG_KGDB_SERIAL_CONSOLE=y and kgdboc was passed on the kernel command line. > kgdb_handle_exception doesn't seem to check whether the debugger is active. > > > The following (totally untested) diff is simpler for arm64, but again, I'm > > not sure we even have a problem here. > > This diff also fixes the problem. I don't have a strong preference for either > approach, so I can revise the patch with this approach instead if you'd prefer > that.
I'll merge the arm64 diff I proposed. Could you repost the ARM part please?
> > On which systems have you managed to reproduce this and how? > > I first reproduced this on a Raspberry Pi. The recommended distro, Raspbian, > distributes a kernel compiled with CONFIG_KGDB=y, CONFIG_KGDB_KDB=y, and > CONFIG_KDB_KEYBOARD=y, so it was sufficient to have a keyboard plugged in. > However, I also reproduced it by booting with kgdboc on the command line, as > CONFIG_KGDB_SERIAL_CONSOLE was also enabled. Additionally, I reproduced it and > then verified that my patch fixed it on self-compiled kernels.
I think enabling and activating kgdb by default is a pretty crazy thing to do, but I agree that we shouldn't allow userspace to trap into it either.
Once you repost the ARM patches, we can look at getting them merged via rmk.
Cheers,
Will
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