kernel.git/arch/powerpc/kernel/irq.c, branch linux-5.10.y

powerpc/kuap: Restore AMR after replaying soft interrupts

2021-03-04T10:38:06Z

[ Upstream commit 60a707d0c99aff4eadb7fd334c5fd21df386723e ] Since de78a9c42a79 ("powerpc: Add a framework for Kernel Userspace Access Protection"), user access helpers call user_{read|write}_access_{begin|end} when user space access is allowed. Commit 890274c2dc4c ("powerpc/64s: Implement KUAP for Radix MMU") made the mentioned helpers program a AMR special register to allow such access for a short period of time, most of the time AMR is expected to block user memory access by the kernel. Since the code accesses the user space memory, unsafe_get_user() calls might_fault() which calls arch_local_irq_restore() if either CONFIG_PROVE_LOCKING or CONFIG_DEBUG_ATOMIC_SLEEP is enabled. arch_local_irq_restore() then attempts to replay pending soft interrupts as KUAP regions have hardware interrupts enabled. If a pending interrupt happens to do user access (performance interrupts do that), it enables access for a short period of time so after returning from the replay, the user access state remains blocked and if a user page fault happens - "Bug: Read fault blocked by AMR!" appears and SIGSEGV is sent. An example trace: Bug: Read fault blocked by AMR! WARNING: CPU: 0 PID: 1603 at /home/aik/p/kernel/arch/powerpc/include/asm/book3s/64/kup-radix.h:145 CPU: 0 PID: 1603 Comm: amr Not tainted 5.10.0-rc6_v5.10-rc6_a+fstn1 #24 NIP: c00000000009ece8 LR: c00000000009ece4 CTR: 0000000000000000 REGS: c00000000dc63560 TRAP: 0700 Not tainted (5.10.0-rc6_v5.10-rc6_a+fstn1) MSR: 8000000000021033 CR: 28002888 XER: 20040000 CFAR: c0000000001fa928 IRQMASK: 1 GPR00: c00000000009ece4 c00000000dc637f0 c000000002397600 000000000000001f GPR04: c0000000020eb318 0000000000000000 c00000000dc63494 0000000000000027 GPR08: c00000007fe4de68 c00000000dfe9180 0000000000000000 0000000000000001 GPR12: 0000000000002000 c0000000030a0000 0000000000000000 0000000000000000 GPR16: 0000000000000000 0000000000000000 0000000000000000 bfffffffffffffff GPR20: 0000000000000000 c0000000134a4020 c0000000019c2218 0000000000000fe0 GPR24: 0000000000000000 0000000000000000 c00000000d106200 0000000040000000 GPR28: 0000000000000000 0000000000000300 c00000000dc63910 c000000001946730 NIP __do_page_fault+0xb38/0xde0 LR __do_page_fault+0xb34/0xde0 Call Trace: __do_page_fault+0xb34/0xde0 (unreliable) handle_page_fault+0x10/0x2c --- interrupt: 300 at strncpy_from_user+0x290/0x440 LR = strncpy_from_user+0x284/0x440 strncpy_from_user+0x2f0/0x440 (unreliable) getname_flags+0x88/0x2c0 do_sys_openat2+0x2d4/0x5f0 do_sys_open+0xcc/0x140 system_call_exception+0x160/0x240 system_call_common+0xf0/0x27c To fix it save/restore the AMR when replaying interrupts, and also add a check if AMR was not blocked prior to replaying interrupts. Originally found by syzkaller. Fixes: 890274c2dc4c ("powerpc/64s: Implement KUAP for Radix MMU") Signed-off-by: Alexey Kardashevskiy Reviewed-by: Nicholas Piggin [mpe: Use normal commit citation format and add full oops log to change log, move kuap_check_amr() into the restore routine to avoid warnings about unreconciled IRQ state] Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210202091541.36499-1-aik@ozlabs.ru Signed-off-by: Sasha Levin

powerpc/64s: prevent recursive replay_soft_interrupts causing superfluous interrupt

2021-02-03T22:28:46Z

[ Upstream commit 4025c784c573cab7e3f84746cc82b8033923ec62 ] When an asynchronous interrupt calls irq_exit, it checks for softirqs that may have been created, and runs them. Running softirqs enables local irqs, which can replay pending interrupts causing recursion in replay_soft_interrupts. This abridged trace shows how this can occur: ! NIP replay_soft_interrupts LR interrupt_exit_kernel_prepare Call Trace: interrupt_exit_kernel_prepare (unreliable) interrupt_return --- interrupt: ea0 at __rb_reserve_next NIP __rb_reserve_next LR __rb_reserve_next Call Trace: ring_buffer_lock_reserve trace_function function_trace_call ftrace_call __do_softirq irq_exit timer_interrupt ! replay_soft_interrupts interrupt_exit_kernel_prepare interrupt_return --- interrupt: ea0 at arch_local_irq_restore This can not be prevented easily, because softirqs must not block hard irqs, so it has to be dealt with. The recursion is bounded by design in the softirq code because softirq replay disables softirqs and loops around again to check for new softirqs created while it ran, so that's not a problem. However it does mess up interrupt replay state, causing superfluous interrupts when the second replay_soft_interrupts clears a pending interrupt, leaving it still set in the first call in the 'happened' local variable. Fix this by not caching a copy of irqs_happened across interrupt handler calls. Fixes: 3282a3da25bd ("powerpc/64: Implement soft interrupt replay in C") Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20210123061244.2076145-1-npiggin@gmail.com Signed-off-by: Sasha Levin

powerpc/64: irq replay remove decrementer overflow check

2021-01-06T13:56:54Z

[ Upstream commit 59d512e4374b2d8a6ad341475dc94c4a4bdec7d3 ] This is way to catch some cases of decrementer overflow, when the decrementer has underflowed an odd number of times, while MSR[EE] was disabled. With a typical small decrementer, a timer that fires when MSR[EE] is disabled will be "lost" if MSR[EE] remains disabled for between 4.3 and 8.6 seconds after the timer expires. In any case, the decrementer interrupt would be taken at 8.6 seconds and the timer would be found at that point. So this check is for catching extreme latency events, and it prevents those latencies from being a further few seconds long. It's not obvious this is a good tradeoff. This is already a watchdog magnitude event and that situation is not improved a significantly with this check. For large decrementers, it's useless. Therefore remove this check, which avoids a mftb when enabling hard disabled interrupts (e.g., when enabling after coming from hardware interrupt handlers). Perhaps more importantly, it also removes the clunky MSR[EE] vs PACA_IRQ_HARD_DIS incoherency in soft-interrupt replay which simplifies the code. Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20201107014336.2337337-1-npiggin@gmail.com Signed-off-by: Sasha Levin

powerpc: Remove get_tb_or_rtc()

2020-10-08T10:17:14Z

601 is gone, get_tb_or_rtc() is equivalent to get_tb(). Replace the former by the later. Signed-off-by: Christophe Leroy Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/3e8a13ee83418630c753c30cb722ae682d5b2d39.1601362098.git.christophe.leroy@csgroup.eu

powerpc/64: make restore_interrupts 64e only

2020-10-06T12:22:24Z

This is not used by 64s. Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200915114650.3980244-5-npiggin@gmail.com

powerpc/64e: remove 64s specific interrupt soft-mask code

2020-10-06T12:22:23Z

Since the assembly soft-masking code was moved to 64e specific, there are some 64s specific interrupt types still there. Remove them. Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200915114650.3980244-4-npiggin@gmail.com

powerpc/64e: remove PACA_IRQ_EE_EDGE

2020-10-06T12:22:23Z

This is not used anywhere. Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200915114650.3980244-3-npiggin@gmail.com

powerpc/64: fix irq replay pt_regs->softe value

2020-10-06T12:22:23Z

Replayed interrupts get an "artificial" struct pt_regs constructed to pass to interrupt handler functions. This did not get the softe field set correctly, it's as though the interrupt has hit while irqs are disabled. It should be IRQS_ENABLED. This is possibly harmless, asynchronous handlers should not be testing if irqs were disabled, but it might be possible for example some code is shared with synchronous or NMI handlers, and it makes more sense if debug output looks at this. Fixes: 3282a3da25bd ("powerpc/64: Implement soft interrupt replay in C") Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200915114650.3980244-2-npiggin@gmail.com

powerpc/64: fix irq replay missing preempt

2020-10-06T12:22:23Z

Prior to commit 3282a3da25bd ("powerpc/64: Implement soft interrupt replay in C"), replayed interrupts returned by the regular interrupt exit code, which performs preemption in case an interrupt had set need_resched. This logic was missed by the conversion. Adding preempt_disable/enable around the interrupt replay and final irq enable will reschedule if needed. Fixes: 3282a3da25bd ("powerpc/64: Implement soft interrupt replay in C") Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200915114650.3980244-1-npiggin@gmail.com

powerpc/64s: Move HMI IRQ stat from percpu variable to paca.

2020-07-29T13:47:53Z

With the proposed change in percpu bootmem allocator to use page mapping [1], the percpu first chunk memory area can come from vmalloc ranges. This makes the HMI (Hypervisor Maintenance Interrupt) handler crash the kernel whenever percpu variable is accessed in real mode. This patch fixes this issue by moving the HMI IRQ stat inside paca for safe access in realmode. [1] https://lore.kernel.org/linuxppc-dev/20200608070904.387440-1-aneesh.kumar@linux.ibm.com/ Suggested-by: Aneesh Kumar K.V Signed-off-by: Mahesh Salgaonkar Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/159290806973.3642154.5244613424529764050.stgit@jupiter