@@ -311,6 +311,23 @@ void replay_soft_interrupts(void)
}
}
+#if defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_PPC_KUAP)
+static inline void replay_soft_interrupts_irqrestore(void)
+{
+ unsigned long kuap_state = get_kuap();
+
+ if (kuap_state != AMR_KUAP_BLOCKED)
+ set_kuap(AMR_KUAP_BLOCKED);
+
+ replay_soft_interrupts();
+
+ if (kuap_state != AMR_KUAP_BLOCKED)
+ set_kuap(kuap_state);
+}
+#else
+#define replay_soft_interrupts_irqrestore() replay_soft_interrupts()
+#endif
+
notrace void arch_local_irq_restore(unsigned long mask)
{
unsigned char irq_happened;
@@ -320,6 +337,14 @@ notrace void arch_local_irq_restore(unsigned long mask)
if (mask)
return;
+ /*
+ * It fires if anything calls local_irq_enable or restore when
+ * KUAP is enabled, and the code handles that just fine by saving
+ * and re-locking AMR but we would like to remove those calls,
+ * hence the warning.
+ */
+ kuap_check_amr();
+
/*
* From this point onward, we can take interrupts, preempt,
* etc... unless we got hard-disabled. We check if an event
@@ -373,7 +398,7 @@ notrace void arch_local_irq_restore(unsigned long mask)
irq_soft_mask_set(IRQS_ALL_DISABLED);
trace_hardirqs_off();
- replay_soft_interrupts();
+ replay_soft_interrupts_irqrestore();
local_paca->irq_happened = 0;
trace_hardirqs_on();
Since de78a9c "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. 890274c "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. This saves/restores AMR when replaying interrupts. This adds a check if AMR was not blocked when before replaying interrupts. Found by syzkaller. The call stack for the bug is: copy_from_user_nofault+0xf8/0x250 perf_callchain_user_64+0x3d8/0x8d0 perf_callchain_user+0x38/0x50 get_perf_callchain+0x28c/0x300 perf_callchain+0xb0/0x130 perf_prepare_sample+0x364/0xbf0 perf_event_output_forward+0xe0/0x280 __perf_event_overflow+0xa4/0x240 perf_swevent_hrtimer+0x1d4/0x1f0 __hrtimer_run_queues+0x328/0x900 hrtimer_interrupt+0x128/0x350 timer_interrupt+0x180/0x600 replay_soft_interrupts+0x21c/0x4f0 arch_local_irq_restore+0x94/0x150 lock_is_held_type+0x140/0x200 ___might_sleep+0x220/0x330 __might_fault+0x88/0x120 do_strncpy_from_user+0x108/0x2b0 strncpy_from_user+0x1d0/0x2a0 getname_flags+0x88/0x2c0 do_sys_openat2+0x2d4/0x5f0 do_sys_open+0xcc/0x140 system_call_exception+0x160/0x240 system_call_common+0xf0/0x27c Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru> Reviewed-by: Nicholas Piggin <npiggin@gmail.com> --- Changes: v3: * do not block/unblock if AMR was blocked * reverted move of AMR_KUAP_*** * added kuap_check_amr v2: * fixed compile on hash * moved get/set to arch_local_irq_restore * block KUAP before replaying --- This is an example: ------------[ cut here ]------------ 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 __do_page_fau Modules linked in: 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 <SF,ME,IR,DR,RI,LE> 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 [c00000000009ece8] __do_page_fault+0xb38/0xde0 LR [c00000000009ece4] __do_page_fault+0xb34/0xde0 Call Trace: [c00000000dc637f0] [c00000000009ece4] __do_page_fault+0xb34/0xde0 (unreliable) [c00000000dc638a0] [c00000000000c968] handle_page_fault+0x10/0x2c --- interrupt: 300 at strncpy_from_user+0x290/0x440 LR = strncpy_from_user+0x284/0x440 [c00000000dc63ba0] [c000000000c3dcb0] strncpy_from_user+0x2f0/0x440 (unreliable) [c00000000dc63c30] [c00000000068b888] getname_flags+0x88/0x2c0 [c00000000dc63c90] [c000000000662a44] do_sys_openat2+0x2d4/0x5f0 [c00000000dc63d30] [c00000000066560c] do_sys_open+0xcc/0x140 [c00000000dc63dc0] [c000000000045e10] system_call_exception+0x160/0x240 [c00000000dc63e20] [c00000000000da60] system_call_common+0xf0/0x27c Instruction dump: 409c0048 3fe2ff5b 3bfff128 fac10060 fae10068 482f7a85 60000000 3c62ff5b 7fe4fb78 3863f250 4815bbd9 60000000 <0fe00000> 3c62ff5b 3863f2b8 4815c8b5 irq event stamp: 254 hardirqs last enabled at (253): [<c000000000019550>] arch_local_irq_restore+0xa0/0x150 hardirqs last disabled at (254): [<c000000000008a10>] data_access_common_virt+0x1b0/0x1d0 softirqs last enabled at (0): [<c0000000001f6d5c>] copy_process+0x78c/0x2120 softirqs last disabled at (0): [<0000000000000000>] 0x0 ---[ end trace ba98aec5151f3aeb ]--- --- arch/powerpc/kernel/irq.c | 27 ++++++++++++++++++++++++++- 1 file changed, 26 insertions(+), 1 deletion(-)