linux.git/arch/s390/kernel/entry.S, branch v6.9

s390/mm: Fix NULL pointer dereference

2024-04-17T15:26:34+00:00

The recently added check to figure out if a fault happened on gmap ASCE
dereferences the gmap pointer in lowcore without checking that it is not
NULL. For all non-KVM processes the pointer is NULL, so that some value
from lowcore will be read. With the current layouts of struct gmap and
struct lowcore the read value (aka ASCE) is zero, so that this doesn't lead
to any observable bug; at least currently.

Fix this by adding the missing NULL pointer check.

Fixes: 64c3431808bd ("s390/entry: compare gmap asce to determine guest/host fault")
Signed-off-by: Sven Schnelle 
Reviewed-by: Claudio Imbrenda 
Reviewed-by: Heiko Carstens 
Signed-off-by: Alexander Gordeev

s390/entry: align system call table on 8 bytes

2024-04-03T13:00:20+00:00

Align system call table on 8 bytes. With sys_call_table entry size
of 8 bytes that eliminates the possibility of a system call pointer
crossing cache line boundary.

Cc: stable@kernel.org
Suggested-by: Ulrich Weigand 
Reviewed-by: Alexander Gordeev 
Signed-off-by: Sumanth Korikkar 
Signed-off-by: Vasily Gorbik

s390/entry: compare gmap asce to determine guest/host fault

2024-03-17T18:08:50+00:00

With the current implementation, there are some cornercases where
a host fault would be treated as a guest fault, for example
when the sie instruction causes a program check. Therefore store
the gmap asce in ptregs, and use that to compare the primary asce
from the fault instead of matching instruction addresses.

Suggested-by: Heiko Carstens 
Signed-off-by: Sven Schnelle 
Signed-off-by: Heiko Carstens

s390/entry: remove OUTSIDE macro

2024-03-17T18:08:49+00:00

With only one OUTSIDE user left, remove the macro and move the code
directly to the machine check handler. This has the advantage that
it is much easier to determine which registers are used.

Signed-off-by: Sven Schnelle 
Reviewed-by: Heiko Carstens 
Signed-off-by: Heiko Carstens

s390/entry: add CIF_SIE flag and remove sie64a() address check

2024-03-17T18:08:49+00:00

When a program check, interrupt or machine check is triggered, the
PSW address is compared to a certain range of the sie64a() function
to figure out whether SIE was interrupted and a cleanup of SIE is
needed.

This doesn't work with kprobes: If kprobes probes an instruction, it
copies the instruction to the kprobes instruction page and overwrites the
original instruction with an undefind instruction (Opcode 00). When this
instruction is hit later, kprobes single-steps the instruction on the
kprobes_instruction page.

However, if this instruction is a relative branch instruction it will now
point to a different location in memory due to being moved to the kprobes
instruction page. If the new branch target points into sie64a() the kernel
assumes it interrupted SIE when processing the breakpoint and will crash
trying to access the SIE control block.

Instead of comparing the address, introduce a new CIF_SIE flag which
indicates whether SIE was interrupted.

Signed-off-by: Sven Schnelle 
Suggested-by: Heiko Carstens 
Reviewed-by: Heiko Carstens 
Signed-off-by: Heiko Carstens

s390/kvm: convert to regular kernel fpu user

2024-02-16T13:30:16+00:00

KVM modifies the kernel fpu's regs pointer to its own area to implement its
custom version of preemtible kernel fpu context. With general support for
preemptible kernel fpu context there is no need for the extra complexity in
KVM code anymore.

Therefore convert KVM to a regular kernel fpu user. In particular this
means that all TIF_FPU checks can be removed, since the fpu register
context will never be changed by other kernel fpu users, and also the fpu
register context will be restored if a thread is preempted.

Reviewed-by: Claudio Imbrenda 
Signed-off-by: Heiko Carstens

s390/fpu: convert FPU CIF flag to regular TIF flag

2024-02-16T13:30:15+00:00

The FPU state, as represented by the CIF_FPU flag reflects the FPU state of
a task, not the CPU it is running on. Therefore convert the flag to a
regular TIF flag.

This removes the magic in switch_to() where a save_fpu_regs() call for the
currently (previous) running task sets the per-cpu CIF_FPU flag, which is
required to restore FPU register contents of the next task, when it returns
to user space.

Signed-off-by: Heiko Carstens

s390/fpu: move, rename, and merge header files

2024-02-16T13:30:14+00:00

Move, rename, and merge the fpu and vx header files. This way fpu header
files have a consistent naming scheme (fpu*.h).

Also get rid of the fpu subdirectory and move header files to asm
directory, so that all fpu and vx header files can be found at the same
location.

Merge internal.h header file into other header files, since the internal
helpers are used at many locations. so those helper functions are really
not internal.

Signed-off-by: Heiko Carstens

s390/nmi: remove register validation code

2024-02-16T13:30:14+00:00

Remove the historic machine check handler code which validates registers.
Registers are automatically validated as part of the machine check handling
sequence (see Principles of Operation, Machine-Check Handling chapter,
Validation).

Signed-off-by: Heiko Carstens

s390/switch_to: use generic header file

2024-02-12T14:03:33+00:00

Move the switch_to() implementation to process.c and use the generic
switch_to.h header file instead, like some other architectures.

This addresses also the oddity that the old switch_to() implementation
assigns the return value of __switch_to() to 'prev' instead of 'last',
like it should.

Remove also all includes of switch_to.h from C files, except process.c.

Acked-by: Alexander Gordeev 
Signed-off-by: Heiko Carstens