linux-toradex.git/arch/powerpc/kernel/interrupt_64.S, branch v5.17

powerpc/64s: Mask SRR0 before checking against the masked NIP

2022-01-17T23:25:18+00:00

Commit 314f6c23dd8d ("powerpc/64s: Mask NIP before checking against
SRR0") masked off the low 2 bits of the NIP value in the interrupt
stack frame in case they are non-zero and mis-compare against a SRR0
register value of a CPU which always reads back 0 from the 2 low bits
which are reserved.

This now causes the opposite problem that an implementation which does
implement those bits in SRR0 will mis-compare against the masked NIP
value in which they have been cleared. QEMU is one such implementation,
and this is allowed by the architecture.

This can be triggered by sigfuz by setting low bits of PT_NIP in the
signal context.

Fix this for now by masking the SRR0 bits as well. Cleaner is probably
to sanitise these values before putting them in registers or stack, but
this is the quick and backportable fix.

Fixes: 314f6c23dd8d ("powerpc/64s: Mask NIP before checking against SRR0")
Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20220117134403.2995059-1-npiggin@gmail.com

powerpc/64s: Use EMIT_WARN_ENTRY for SRR debug warnings

2021-12-24T23:56:01+00:00

When CONFIG_PPC_RFI_SRR_DEBUG=y we check the SRR values before returning
from interrupts. This is done in asm using EMIT_BUG_ENTRY, and passing
BUGFLAG_WARNING.

However that fails to create an exception table entry for the warning,
and so do_program_check() fails the exception table search and proceeds
to call _exception(), resulting in an oops like:

  Oops: Exception in kernel mode, sig: 5 [#1]
  LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
  Modules linked in:
  CPU: 2 PID: 1204 Comm: sigreturn_unali Tainted: P                  5.16.0-rc2-00194-g91ca3d4f77c5 #12
  NIP:  c00000000000c5b0 LR: 0000000000000000 CTR: 0000000000000000
  ...
  NIP [c00000000000c5b0] system_call_common+0x150/0x268
  LR [0000000000000000] 0x0
  Call Trace:
  [c00000000db73e10] [c00000000000c558] system_call_common+0xf8/0x268 (unreliable)
  ...
  Instruction dump:
  7cc803a6 888d0931 2c240000 4082001c 38800000 988d0931 e8810170 e8a10178
  7c9a03a6 7cbb03a6 7d7a02a6 e9810170 <7f0b6088> 7d7b02a6 e9810178 7f0b6088

We should instead use EMIT_WARN_ENTRY, which creates an exception table
entry for the warning, allowing the warning to be correctly recognised,
and the code to resume after printing the warning.

Note however that because this warning is buried deep in the interrupt
return path, we are not able to recover from it (due to MSR_RI being
clear), so we still end up in die() with an unrecoverable exception.

Fixes: 59dc5bfca0cb ("powerpc/64s: avoid reloading (H)SRR registers if they are still valid")
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20211221135101.2085547-2-mpe@ellerman.id.au

powerpc/64s: Mask NIP before checking against SRR0

2021-12-24T23:55:55+00:00

When CONFIG_PPC_RFI_SRR_DEBUG=y we check that NIP and SRR0 match when
returning from interrupts. This can trigger falsely if NIP has either of
its two low bits set via sigreturn or ptrace, while SRR0 has its low two
bits masked in hardware.

As a quick fix make sure to mask the low bits before doing the check.

Fixes: 59dc5bfca0cb ("powerpc/64s: avoid reloading (H)SRR registers if they are still valid")
Reported-by: Sachin Sant 
Signed-off-by: Michael Ellerman 
Tested-by: Sachin Sant 
Link: https://lore.kernel.org/r/20211221135101.2085547-1-mpe@ellerman.id.au

powerpc/64/asm: Do not reassign labels

2021-12-23T11:35:12+00:00

The LLVM integrated assembler really does not like us reassigning things
to the same label:

:7:9: error: invalid reassignment of non-absolute variable 'fs_label'

This happens across a bunch of platforms:
https://github.com/ClangBuiltLinux/linux/issues/1043
https://github.com/ClangBuiltLinux/linux/issues/1008
https://github.com/ClangBuiltLinux/linux/issues/920
https://github.com/ClangBuiltLinux/linux/issues/1050

There is no hope of getting this fixed in LLVM (see
https://github.com/ClangBuiltLinux/linux/issues/1043#issuecomment-641571200
and https://bugs.llvm.org/show_bug.cgi?id=47798#c1 )
so if we want to build with LLVM_IAS, we need to hack
around it ourselves.

For us the big problem comes from this:

\#define USE_FIXED_SECTION(sname)				\
	fs_label = start_##sname;				\
	fs_start = sname##_start;				\
	use_ftsec sname;

\#define USE_TEXT_SECTION()
	fs_label = start_text;					\
	fs_start = text_start;					\
	.text

and in particular fs_label.

This works around it by not setting those 'variables' and requiring
that users of the variables instead track for themselves what section
they are in. This isn't amazing, by any stretch, but it gets us further
in the compilation.

Note that even though users have to keep track of the section, using
a wrong one produces an error with both binutils and llvm which prevents
from using wrong section at the compile time:

llvm error example:

AS      arch/powerpc/kernel/head_64.o
:0: error: Cannot represent a difference across sections
make[3]: *** [/home/aik/p/kernels-llvm/llvm/scripts/Makefile.build:388: arch/powerpc/kernel/head_64.o] Error 1

binutils error example:

/home/aik/p/kernels-llvm/llvm/arch/powerpc/kernel/exceptions-64s.S: Assembler messages:
/home/aik/p/kernels-llvm/llvm/arch/powerpc/kernel/exceptions-64s.S:1974: Error: can't resolve `system_call_common' {.text section} - `start_r
eal_vectors' {.head.text.real_vectors section}
make[3]: *** [/home/aik/p/kernels-llvm/llvm/scripts/Makefile.build:388: arch/powerpc/kernel/head_64.o] Error 1

Signed-off-by: Daniel Axtens 
Signed-off-by: Alexey Kardashevskiy 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20211221055904.555763-5-aik@ozlabs.ru

powerpc: flexible GPR range save/restore macros

2021-11-29T12:15:20+00:00

Introduce macros that operate on a (start, end) range of GPRs, which
reduces lines of code and need to do mental arithmetic while reading the
code.

Signed-off-by: Nicholas Piggin 
Reviewed-by: Segher Boessenkool 
Reviewed-by: Christophe Leroy 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20211022061322.2671178-1-npiggin@gmail.com

powerpc/64s: system call scv tabort fix for corrupt irq soft-mask state

2021-09-13T12:34:11+00:00

If a system call is made with a transaction active, the kernel
immediately aborts it and returns. scv system calls disable irqs even
earlier in their interrupt handler, and tabort_syscall does not fix this
up.

This can result in irq soft-mask state being messed up on the next
kernel entry, and crashing at BUG_ON(arch_irq_disabled_regs(regs)) in
the kernel exit handlers, or possibly worse.

This can't easily be fixed in asm because at this point an async irq may
have hit, which is soft-masked and marked pending. The pending interrupt
has to be replayed before returning to userspace. The fix is to move the
tabort_syscall code to C in the main syscall handler, and just skip the
system call but otherwise return as usual, which will take care of the
pending irqs. This also does a bunch of other things including possible
signal delivery to the process, but the doomed transaction should still
be aborted when it is eventually returned to.

The sc system call path is changed to use the new C function as well to
reduce code and path differences. This slows down how quickly system
calls are aborted when called while a transaction is active, which could
potentially impact TM performance. But making any system call is already
bad for performance, and TM is on the way out, so go with simpler over
faster.

Fixes: 7fa95f9adaee7 ("powerpc/64s: system call support for scv/rfscv instructions")
Reported-by: Eirik Fuller 
Signed-off-by: Nicholas Piggin 
[mpe: Use #ifdef rather than IS_ENABLED() to fix build error on 32-bit]
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20210903125707.1601269-1-npiggin@gmail.com

powerpc/64e: Fix system call illegal mtmsrd instruction

2021-07-06T09:58:54+00:00

BookE does not have mtmsrd, switch to use wrteei to enable MSR[EE].

Fixes: dd152f70bdc1 ("powerpc/64s: system call avoid setting MSR[RI] until we set MSR[EE]")
Reported-by: Christian Zigotzky 
Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20210706051310.608992-1-npiggin@gmail.com

powerpc/64s: move ret_from_fork etc above __end_soft_masked

2021-06-30T12:21:20+00:00

Code which runs with interrupts enabled should be moved above
__end_soft_masked where possible, because maskable interrupts that hit
below that symbol will need to consult the soft mask table, which is an
extra cost.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20210630074621.2109197-10-npiggin@gmail.com

powerpc/64s/interrupt: clean up interrupt return labels

2021-06-30T12:21:20+00:00

Normal kernel-interrupt exits can get interrupt_return_srr_user_restart
in their backtrace, which is an unusual and notable function, and it is
part of the user-interrupt exit path, which is doubly confusing.

Add non-local labels for both user and kernel interrupt exit cases to
address this and make the user and kernel cases more symmetric. Also get
rid of an unused label.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20210630074621.2109197-9-npiggin@gmail.com

powerpc/64/interrupt: add missing kprobe annotations on interrupt exit symbols

2021-06-30T12:21:20+00:00

If one interrupt exit symbol must not be kprobed, none of them can be,
without more justification for why it's safe. Disallow kprobing on any
of the (non-local) labels in the exit paths.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/20210630074621.2109197-8-npiggin@gmail.com