On 6/15/21 4:32 AM, Bruno Piazera Larsen wrote:
On 14/06/2021 19:37, Richard Henderson wrote:
On 6/14/21 12:16 PM, Bruno Larsen (billionai) wrote:
This patch changes ppc_cpu_get_phys_page_debug so that it is now
able to translate both, priviledged and real mode addresses
independently of whether the CPU executing it has those permissions
This was mentioned by Fabiano as something that would be very useful to
help with debugging, but could possibly constitute a security issue if
that debug function can be called in some way by prodution code. the
solution was implemented such that it would be trivial to wrap it around
ifdefs for building only with --enable-debug, for instance, but we are
not sure this is the best approach, hence why it is an RFC.
Suggested-by: Fabiano Rosas<faro...@linux.ibm.com>
Signed-off-by: Bruno Larsen (billionai)<bruno.lar...@eldorado.org.br>
---
target/ppc/mmu_helper.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
I think the first part is unnecessary. Either the cpu is in supervisor mode or it
isn't, and gdb should use the correct address space. If you really want to force
supervisor lookup from a guest that is paused in usermode, I suppose you could force
MSR.PR=1 while you're performing the access and set it back afterward.
I don't see why GDB should not be able to see supervisor level addresses just because the
CPU can't.
Because then when you are debugging, you then don't know whether the address is actually
accessible in the current cpu context.
I think the second part is actively wrong -- real-mode address lookup will (for the most
part) always succeed. Moreover, the gdb user will have no idea that you've silently
changed addressing methods.
I disagree. Real-mode address will mostly fail, since during the boot process Linux
kernels set the MMU to use only virtual addresses, so real mode addresses only work when
debugging the firmware or the early setup of the kernel. After that, GDB can basically
only see virtual addresses.
Exactly. But you changed that so that any unmapped address will re-try with real-mode,
which (outside of hv) simply maps real->physical and returns the input.
One should have to perform some special action to see addresses in a different cpu
context. I don't think that gdb supports such a special action at the moment. If you
want that feature though, that's where you should start.
r~
