When a signal is being delivered, the kernel needs to make accesses to
userspace. These accesses could encounter an access error, in which case
the signal delivery itself will trigger a segfault. Usually this would
result in the kernel killing the process. But in the case of a SEGV signal
handler being configured, the failure of the first signal delivery will
result in *another* signal getting delivered. The second signal may
succeed if another thread has resolved the issue that triggered the
segfault (i.e. a well timed mprotect()/mmap()), or the second signal is
being delivered to another stack (i.e. an alt stack).

On x86, in the non-shadow stack case, all the accesses to userspace are
done before changes to the registers (in pt_regs). The operation is
aborted when an access error occurs, so although there may be writes done
for the first signal, control flow changes for the signal (regs->ip,
regs->sp, etc) are not committed until all the accesses have already
completed successfully. This means that the second signal will be
delivered as if it happened at the time of the first signal. It will
effectively replace the first aborted signal, overwriting the half-written
frame of the aborted signal. So on sigreturn from the second signal,
control flow will resume happily from the point of control flow where the
original signal was delivered.

The problem is, when shadow stack is active, the shadow stack SSP
register/MSR is updated *before* some of the userspace accesses. This
means if the earlier accesses succeed and the later ones fail, the second
signal will not be delivered at the same spot on the shadow stack as the
first one. So on sigreturn from the second signal, the SSP will be
pointing to the wrong location on the shadow stack (off by a frame).

Pengfei privately reported that while using a shadow stack enabled glibc,
the “signal06” test in the LTP test-suite hung. It turns out it is
testing the above described double signal scenario. When this test was
compiled with shadow stack, the first signal pushed a shadow stack
sigframe, then the second pushed another. When the second signal was
handled, the SSP was at the first shadow stack signal frame instead of
the original location. The test then got stuck as the #CP from the twice
incremented SSP was incorrect and generated segfaults in a loop.

Fix this by adjusting the SSP register only after any userspace accesses,
such that there can be no failures after the SSP is adjusted. Do this by
moving the shadow stack sigframe push logic to happen after all other
userspace accesses.

Note, sigreturn (as opposed to the signal delivery dealt with in this
patch) has ordering behavior that could lead to similar failures. The
ordering issues there extend beyond shadow stack to include the alt stack
restoration. Fixing that would require cross-arch changes, and the
ordering today does not cause any known test or apps breakages. So leave
it as is, for now.

[ dhansen: minor changelog/subject tweak ]

Fixes: 05e36022c054 ("x86/shstk: Handle signals for shadow stack")
Reported-by: Pengfei Xu <pengfei.xu@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Cc:stable@vger.kernel.org
Link: https://lore.kernel.org/all/20231107182251.91276-1-rick.p.edgecombe%40intel.com
Link: https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/signal/signal06.c

The protocol version number note is between the protocol version table and
the memory layout section. As such, Sphinx renders the note directive not
only on the actual note, but until the end of doc.

Indent the directive so that only the actual protocol version number
note is rendered as such.

Fixes: 2c33c27fd603 ("x86/boot: Introduce kernel_info")
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231106101206.76487-2-bagasdotme@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Add myself as Intel TDX maintainer.

I drove upstreaming most of TDX code so far and I will continue
working on TDX for foreseeable future.

[ dhansen: * Add myself as a reviewer too
* Swap Maintained=>Supported. I double
checked Kirill is still being paid
* Add drivers/virt/coco/tdx-guest ]

Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Acked-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/all/20231101233314.2567-1-kirill.shutemov%40linux.intel.com

Pull misc x86 fixes from Ingo Molnar:

- Fix a possible CPU hotplug deadlock bug caused by the new TSC
synchronization code

- Fix a legacy PIC discovery bug that results in device troubles on
affected systems, such as non-working keybards, etc

- Add a new Intel CPU model number to <asm/intel-family.h>

* tag 'x86-urgent-2023-10-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/tsc: Defer marking TSC unstable to a worker
x86/i8259: Skip probing when ACPI/MADT advertises PCAT compatibility
x86/cpu: Add model number for Intel Arrow Lake mobile processor

Pull irq fix from Ingo Molnar:
"Restore unintentionally lost quirk settings in the GIC irqchip driver,
which broke certain devices"

* tag 'irq-urgent-2023-10-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
irqchip/gic-v3-its: Don't override quirk settings with default values

Tetsuo reported the following lockdep splat when the TSC synchronization
fails during CPU hotplug:

tsc: Marking TSC unstable due to check_tsc_sync_source failed

WARNING: inconsistent lock state
inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage.
ffffffff8cfa1c78 (watchdog_lock){?.-.}-{2:2}, at: clocksource_watchdog+0x23/0x5a0
{IN-HARDIRQ-W} state was registered at:
_raw_spin_lock_irqsave+0x3f/0x60
clocksource_mark_unstable+0x1b/0x90
mark_tsc_unstable+0x41/0x50
check_tsc_sync_source+0x14f/0x180
sysvec_call_function_single+0x69/0x90

Possible unsafe locking scenario:
lock(watchdog_lock);
<Interrupt>
lock(watchdog_lock);

stack backtrace:
_raw_spin_lock+0x30/0x40
clocksource_watchdog+0x23/0x5a0
run_timer_softirq+0x2a/0x50
sysvec_apic_timer_interrupt+0x6e/0x90

The reason is the recent conversion of the TSC synchronization function
during CPU hotplug on the control CPU to a SMP function call. In case
that the synchronization with the upcoming CPU fails, the TSC has to be
marked unstable via clocksource_mark_unstable().

clocksource_mark_unstable() acquires 'watchdog_lock', but that lock is
taken with interrupts enabled in the watchdog timer callback to minimize
interrupt disabled time. That's obviously a possible deadlock scenario,

Before that change the synchronization function was invoked in thread
context so this could not happen.

As it is not crucical whether the unstable marking happens slightly
delayed, defer the call to a worker thread which avoids the lock context
problem.

Fixes: 9d349d47f0e3 ("x86/smpboot: Make TSC synchronization function call based")
Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/87zg064ceg.ffs@tglx

Pull perf event fix from Ingo Molnar:
"Fix a potential NULL dereference bug"

* tag 'perf-urgent-2023-10-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
perf/core: Fix potential NULL deref

When splitting the allocation of the ITS node from its configuration,
some of the default settings were kept in the latter instead of
being moved to the former.

This has the side effect of negating some of the quirk detections that
have happened in between, amongst which the dreaded Synquacer hack
(that also affect Dominic's TI platform).

Move the initialisation of these fields early, so that they can again be
overriden by the Synquacer quirk.

Fixes: 9585a495ac93 ("irqchip/gic-v3-its: Split allocation from initialisation of its_node")
Reported by: Dominic Rath <dominic.rath@ibv-augsburg.net>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Dominic Rath <dominic.rath@ibv-augsburg.net>
Link: https://lore.kernel.org/r/20231024084831.GA3788@JADEVM-DRA
Link: https://lore.kernel.org/r/20231024143431.2144579-1-maz@kernel.org

David and a few others reported that on certain newer systems some legacy
interrupts fail to work correctly.

Debugging revealed that the BIOS of these systems leaves the legacy PIC in
uninitialized state which makes the PIC detection fail and the kernel
switches to a dummy implementation.

Unfortunately this fallback causes quite some code to fail as it depends on
checks for the number of legacy PIC interrupts or the availability of the
real PIC.

In theory there is no reason to use the PIC on any modern system when
IO/APIC is available, but the dependencies on the related checks cannot be
resolved trivially and on short notice. This needs lots of analysis and
rework.

The PIC detection has been added to avoid quirky checks and force selection
of the dummy implementation all over the place, especially in VM guest
scenarios. So it's not an option to revert the relevant commit as that
would break a lot of other scenarios.

One solution would be to try to initialize the PIC on detection fail and
retry the detection, but that puts the burden on everything which does not
have a PIC.

Fortunately the ACPI/MADT table header has a flag field, which advertises
in bit 0 that the system is PCAT compatible, which means it has a legacy
8259 PIC.

Evaluate that bit and if set avoid the detection routine and keep the real
PIC installed, which then gets initialized (for nothing) and makes the rest
of the code with all the dependencies work again.

Fixes: e179f6914152 ("x86, irq, pic: Probe for legacy PIC and set legacy_pic appropriately")
Reported-by: David Lazar <dlazar@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: David Lazar <dlazar@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Cc: stable@vger.kernel.org
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218003
Link: https://lore.kernel.org/r/875y2u5s8g.ffs@tglx

Pull probes fixes from Masami Hiramatsu:

- tracing/kprobes: Fix kernel-doc warnings for the variable length
arguments

- tracing/kprobes: Fix to count the symbols in modules even if the
module name is not specified so that user can probe the symbols in
the modules without module name

* tag 'probes-fixes-v6.6-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing/kprobes: Fix symbol counting logic by looking at modules as well
tracing/kprobes: Fix the description of variable length arguments

Smatch is awesome.

Fixes: 32671e3799ca ("perf: Disallow mis-matched inherited group reads")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Pull irqchip fixes from Marc Zyngier:

- DT binding updates for Renesas r8a779f0 and rzg2l

- Let GICv3 honor the "dma-non-coherent" attribute for systems that
rely on SW guessing what the HW supports

- Fix the RISC-V INTC probing by marking all devices as initialised
at once

- Properly translate interrupt numbers from DT on stm32-exti

- Use irq_data_get_irq_chip_data() in the rzg2l driver instead of
blindly dereferencing the irq_data structure

- Add a MAINTAINERS entry for the various ARM GIC irqchip drivers

- Remove myself as the top-level irqchip/irqdomain maintainer

Link: https://lore.kernel.org/all/20231007121933.3840357-1-maz@kernel.org

For "reasons" Intel has code-named this CPU with a "_H" suffix.

[ dhansen: As usual, apply this and send it upstream quickly to
make it easier for anyone who is doing work that
consumes this. ]

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/20231025202513.12358-1-tony.luck%40intel.com

Pull dma-mapping fix from Christoph Hellwig:

- reduce the initialy dynamic swiotlb size to remove an annoying but
harmless warning from the page allocator (Petr Tesarik)

* tag 'dma-mapping-6.6-2023-10-28' of git://git.infradead.org/users/hch/dma-mapping:
swiotlb: do not try to allocate a TLB bigger than MAX_ORDER pages