VM_PROT_READ|VM_PROT_EXECUTE. The previous default (VM_PROT_ALL)
would cause the following scenario:
- someone attempts to write kernel text (my test was writing
to an offset of /dev/kmem which was known to be in the text
segment, while in single-user mode).
- enter trap() with MMU fault (because of RO pte).
- trap() calls vm_fault(), which looks up vm_map_entry for
fauling address.
- vm_fault interprets write fault and VM_PROT_WRITE (in VM_PROT_ALL)
as COW; new page allocated, data copied to new page, new page
mapped in at trunc_page(<faulting va>).
- wow, look at the fireworks!
Fixes two potential symptoms:
- kernacc() returns TRUE when checking for permission to write
an offset in kernel text, which is bogus, since the text has
been mapped RO by pmap_bootstrap().
- Handling of a stray pointer that attempted to scribble into
kernel text would not be executed properly.
don't do this, kernacc() will bogusly return TRUE for page 0, causing a
NULL pointer dereference in uiomove() when reading /dev/kmem.
Thanks to Scott Reynolds for noticing the problem.
- Fix up usage of MBD_ISPID().
- Ensure that we never deal with a NULL proc, and if our proc has
no pcb, punt. Suggested by Gordon Ross.
- Eliminate some redundant NULL pointer checks in the T_MMUFLT cases;
proc0.p_addr is now initialized early, and we make a single test
for sanity at the top of trap() now.
- Initialize proc0.p_addr just after setting up the kernel stack, to avoid
getting NULL pointers in trap(). Change suggested by Gordon Ross.
- Panic if main() returns.
- Tidy up a couple of comments.
(remaps page read/write/cache-inhibit, does write, restores previous
mapping). Kernel text no longer needs to be read/write with DDB/KGDB
is in the kernel.
Based on a similar module written for the Sun3 port by Gordon Ross,
and modified somewhat by me.
- Offset kernel text one page. Stash the PA of this offset page for
use later.
- Add a few comments.
- Free up some registers earlier in the initialization process.
- Use a `prototc' to set the Translation Control register, rather
than relying on a2 pointing just past the MMU trampoline in the
high page. (Suggested by Charles Hannum.)
- Set VBR to the kernel vector table just before turning on the MMU.
- Just before rebooting, set VBR to 0, which is what the BOOTROM expects
it to be.
kernel setroot(). The device type for network boot is set like any
other device now. Also, call the punit entry point for device drivers
to properly set `bootdev'.
The "options GENERIC" entry in kernel config files is not longer necessary
for "swap generic" kernels. Uses new config constructs which work with
some glue in an old config environment. This code will support new config
with minimal changes.
an unrecognized keyboard produced garbage on keypresses in the kernel,
but worked in the boot program (which has this default). The bug is
that the keymap pointers are unitialized.
- Only pass user trace traps and breakpoints on to trap().
Gets rid of some hair in the trace/breakpoint trap cases.
- Before entering the debugger, switch to a temporary
stack so that the debugger can alter the stack pointer.
- Add glue for KGDB (still not complete).
Some other minor cleanup:
- Protect against some bad pointer derefs.
- Be more a little more verbose when a fatal trap
occurs to aid debugging.
- Only pass user trace traps and breakpoints on to trap().
- Before entering the debugger, switch to a temporary
stack so that the debugger can alter the stack pointer.
- Add glue for KGDB (still not complete).
Clearly mark the MMU enable trampoline code.
cgd