linux-toradex.git/arch/powerpc/kernel/rtas_entry.S, branch v6.4-rc2

powerpc/rtas: Fix RTAS MSR[HV] handling for Cell

2022-08-25T22:41:54+00:00

The semi-recent changes to MSR handling when entering RTAS (firmware)
cause crashes on IBM Cell machines. An example trace:

  kernel tried to execute user page (2fff01a8) - exploit attempt? (uid: 0)
  BUG: Unable to handle kernel instruction fetch
  Faulting instruction address: 0x2fff01a8
  Oops: Kernel access of bad area, sig: 11 [#1]
  BE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=4 NUMA Cell
  Modules linked in:
  CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W          6.0.0-rc2-00433-gede0a8d3307a #207
  NIP:  000000002fff01a8 LR: 0000000000032608 CTR: 0000000000000000
  REGS: c0000000015236b0 TRAP: 0400   Tainted: G        W           (6.0.0-rc2-00433-gede0a8d3307a)
  MSR:  0000000008001002   CR: 00000000  XER: 20000000
  ...
  NIP 0x2fff01a8
  LR  0x32608
  Call Trace:
    0xc00000000143c5f8 (unreliable)
    .rtas_call+0x224/0x320
    .rtas_get_boot_time+0x70/0x150
    .read_persistent_clock64+0x114/0x140
    .read_persistent_wall_and_boot_offset+0x24/0x80
    .timekeeping_init+0x40/0x29c
    .start_kernel+0x674/0x8f0
    start_here_common+0x1c/0x50

Unlike PAPR platforms where RTAS is only used in guests, on the IBM Cell
machines Linux runs with MSR[HV] set but also uses RTAS, provided by
SLOF.

Fix it by copying the MSR[HV] bit from the MSR value we've just read
using mfmsr into the value used for RTAS.

It seems like we could also fix it using an #ifdef CELL to set MSR[HV],
but that doesn't work because it's possible to build a single kernel
image that runs on both Cell native and pseries.

Fixes: b6b1c3ce06ca ("powerpc/rtas: Keep MSR[RI] set when calling RTAS")
Cc: stable@vger.kernel.org # v5.19+
Signed-off-by: Michael Ellerman 
Reviewed-by: Jordan Niethe 
Link: https://lore.kernel.org/r/20220823115952.1203106-2-mpe@ellerman.id.au

powerpc/rtas: Leave MSR[RI] enabled over RTAS call

2022-05-19T13:11:27+00:00

PAPR specifies that RTAS may be called with MSR[RI] enabled if the
calling context is recoverable, and RTAS will manage RI as necessary.
Call the rtas entry point with RI enabled, and add a check to ensure
the caller has RI enabled.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20220308135047.478297-10-npiggin@gmail.com

powerpc/rtas: PACA can be restored directly from SPRG

2022-05-19T13:11:27+00:00

On 64-bit, PACA is saved in a SPRG so it does not need to be saved on
stack. We also don't need to mask off the top bits for real mode
addresses because the architecture does this for us.

Signed-off-by: Nicholas Piggin 
Reviewed-by: Laurent Dufour 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20220308135047.478297-8-npiggin@gmail.com

powerpc/rtas: Call enter_rtas with MSR[EE] disabled

2022-05-19T13:11:27+00:00

Disable MSR[EE] in C code rather than asm.

Signed-off-by: Nicholas Piggin 
Reviewed-by: Laurent Dufour 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20220308135047.478297-5-npiggin@gmail.com

powerpc/rtas: Fix whitespace in rtas_entry.S

2022-05-19T13:11:27+00:00

The code was moved verbatim including whitespace cruft. Fix that.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20220308135047.478297-4-npiggin@gmail.com

powerpc/rtas: Make enter_rtas a nokprobe symbol on 64-bit

2022-05-19T13:11:27+00:00

This symbol is marked nokprobe on 32-bit but not 64-bit, add it.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20220308135047.478297-3-npiggin@gmail.com

powerpc/rtas: Move rtas entry assembly into its own file

2022-05-19T13:11:27+00:00

This makes working on the code a bit easier.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20220308135047.478297-2-npiggin@gmail.com