kernel_optimize_test/arch/powerpc
Alexey Kardashevskiy f5f08edae1 powerpc/kuap: Restore AMR after replaying soft interrupts
[ Upstream commit 60a707d0c99aff4eadb7fd334c5fd21df386723e ]

Since de78a9c42a ("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 890274c2dc ("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 
  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 __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: 890274c2dc ("powerpc/64s: Implement KUAP for Radix MMU")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
[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 <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210202091541.36499-1-aik@ozlabs.ru
Signed-off-by: Sasha Levin <sashal@kernel.org>
2021-03-04 11:38:06 +01:00
..
boot powerpc/boot: Fix build of dts/fsl 2020-12-30 11:54:01 +01:00
configs
crypto
include powerpc/uaccess: Avoid might_fault() when user access is enabled 2021-03-04 11:38:06 +01:00
kernel powerpc/kuap: Restore AMR after replaying soft interrupts 2021-03-04 11:38:06 +01:00
kexec
kvm KVM: PPC: Make the VMX instruction emulation routines static 2021-03-04 11:38:01 +01:00
lib powerpc/64s: fix scv entry fallback flush vs interrupt 2021-01-27 11:55:12 +01:00
math-emu
mm powerpc/mm: Fix verification of MMU_FTR_TYPE_44x 2020-12-30 11:54:16 +01:00
net
oprofile
perf powerpc/perf: Exclude kernel samples while counting events in user space. 2020-12-30 11:54:10 +01:00
platforms powerpc/pseries/dlpar: handle ibm, configure-connector delay status 2021-03-04 11:38:04 +01:00
purgatory
sysdev powerpc: sysdev: add missing iounmap() on error in mpic_msgr_probe() 2021-01-06 14:56:53 +01:00
tools
xmon powerpc/xmon: Change printk() to pr_cont() 2020-12-30 11:54:16 +01:00
Kbuild
Kconfig powerpc/47x: Disable 256k page size 2021-03-04 11:38:01 +01:00
Kconfig.debug
Makefile Kbuild fixes for v5.10 (2nd) 2020-12-06 10:31:39 -08:00
Makefile.postlink