linux.git/arch/powerpc/kernel/process.c, branch v6.6

powerpc/dexcr: Support userspace ROP protection

2023-06-19T07:36:26+00:00

The ISA 3.1B hashst and hashchk instructions use a per-cpu SPR HASHKEYR
to hold a key used in the hash calculation. This key should be different
for each process to make it harder for a malicious process to recreate
valid hash values for a victim process.

Add support for storing a per-thread hash key, and setting/clearing
HASHKEYR appropriately.

Signed-off-by: Benjamin Gray 
Reviewed-by: Russell Currey 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230616034846.311705-6-bgray@linux.ibm.com

powerpc: copy_thread don't set PPR in user interrupt frame regs

2023-04-11T13:13:33+00:00

syscalls do not set the PPR field in their interrupt frame and
return from syscall always sets the default PPR for userspace,
so setting the value in the ret_from_fork frame is not necessary
and mildly inconsistent. Remove it.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230325122904.2375060-9-npiggin@gmail.com

powerpc: copy_thread don't set _TIF_RESTOREALL

2023-04-11T13:13:33+00:00

In the kernel user thread path, don't set _TIF_RESTOREALL because
the thread is required to call kernel_execve() before it returns,
which will set _TIF_RESTOREALL if necessary via start_thread().

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230325122904.2375060-8-npiggin@gmail.com

powerpc: differentiate kthread from user kernel thread start

2023-04-11T13:13:33+00:00

Kernel created user threads start similarly to kernel threads in that
they call a kernel function after first returning from _switch, so
they share ret_from_kernel_thread for this. Kernel threads never return
from that function though, whereas user threads often do (although some
don't, e.g., IO threads).

Split these startup functions in two, and catch kernel threads that
improperly return from their function. This is intended to make the
complicated code a little bit easier to understand.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230325122904.2375060-7-npiggin@gmail.com

powerpc: copy_thread differentiate kthreads and user mode threads

2023-04-11T13:13:33+00:00

When copy_thread is given a kernel function to run in arg->fn, this
does not necessarily mean it is a kernel thread. User threads can be
created this way (e.g., kernel_init, see also x86's copy_thread()).
These threads run a kernel function which may call kernel_execve()
and return, which returns like a userspace exec(2) syscall.

Kernel threads are to  be differentiated with PF_KTHREAD, will always
have arg->fn set, and should never return from that function, instead
calling kthread_exit() to exit.

Create separate paths for the kthread and user kernel thread creation
logic. The kthread path will never exit and does not require a user
interrupt frame, so it gets a minimal stack frame.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230325122904.2375060-6-npiggin@gmail.com

powerpc: use switch frame for ret_from_kernel_thread parameters

2023-04-11T13:13:32+00:00

The kernel thread path in copy_thread creates a user interrupt frame on
stack and stores the function and arg parameters there, and
ret_from_kernel_thread loads them. This is a slightly confusing way to
overload that frame. Non-volatile registers are loaded from the switch
frame, so the parameters can be stored there. The user interrupt frame
is now only used by user threads when they return to user.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230325122904.2375060-4-npiggin@gmail.com

powerpc: copy_thread make ret_from_fork register setup consistent

2023-04-11T13:13:32+00:00

The ret_from_fork code for 64e and 32-bit set r3 for
syscall_exit_prepare the same way that 64s does, so there should
be no need to special-case them in copy_thread.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230325122904.2375060-3-npiggin@gmail.com

powerpc: copy_thread remove unused pkey code

2023-04-11T13:13:32+00:00

The pkey registers (AMR, IAMR) do not get loaded from the switch frame
so it is pointless to save anything there. Remove the dead code.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20230325122904.2375060-2-npiggin@gmail.com

powerpc: Fix a kernel-doc warning

2023-03-14T13:52:09+00:00

The current code provokes a kernel-doc warnings:
  arch/powerpc/kernel/process.c:1606: warning: This comment starts with
  '/**', but isn't a kernel-doc comment. Refer
  Documentation/doc-guide/kernel-doc.rst

Signed-off-by: Bo Liu 
Reviewed-by: Christophe Leroy 
Signed-off-by: Michael Ellerman 
Link: https://msgid.link/20221101015452.3216-1-liubo03@inspur.com

powerpc: Skip stack validation checking alternate stacks if they are not allocated

2023-02-10T11:19:56+00:00

Stack validation in early boot can just bail out of checking alternate
stacks if they are not validated yet. Checking against a NULL stack
could cause NULLish pointer values to be considered valid.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20221216115930.2667772-5-npiggin@gmail.com