Syzkaller reported a sleep in atomic context bug relating to the HASHCHK
handler logic
BUG: sleeping function called from invalid context at
arch/powerpc/kernel/traps.c:1518
in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 25040, name:
syz-executor
preempt_count: 0, expected: 0
RCU nest depth: 0, expected: 0
no locks held by syz-executor/25040.
irq event stamp: 34
hardirqs last enabled at (33): [<c000000000048b38>]
prep_irq_for_enabled_exit arch/powerpc/kernel/interrupt.c:56 [inline]
hardirqs last enabled at (33): [<c000000000048b38>]
interrupt_exit_user_prepare_main+0x148/0x600 arch/powerpc/kernel/interrupt.c:230
hardirqs last disabled at (34): [<c00000000003e6a4>]
interrupt_enter_prepare+0x144/0x4f0 arch/powerpc/include/asm/interrupt.h:176
softirqs last enabled at (0): [<c000000000281954>]
copy_process+0x16e4/0x4750 kernel/fork.c:2436
softirqs last disabled at (0): [<0000000000000000>] 0x0
CPU: 15 PID: 25040 Comm: syz-executor Not tainted
6.5.0-rc5-00001-g3ccdff6bb06d #3
Hardware name: IBM,9105-22A POWER10 (raw) 0x800200 0xf000006 of:IBM,FW1040.00
(NL1040_021) hv:phyp pSeries
Call Trace:
[c0000000a8247ce0] [c00000000032b0e4] __might_resched+0x3b4/0x400
kernel/sched/core.c:10189
[c0000000a8247d80] [c0000000008c7dc8] __might_fault+0xa8/0x170
mm/memory.c:5853
[c0000000a8247dc0] [c00000000004160c] do_program_check+0x32c/0xb20
arch/powerpc/kernel/traps.c:1518
[c0000000a8247e50] [c000000000009b2c] program_check_common_virt+0x3bc/0x3c0
To determine if a trap was caused by a HASHCHK instruction, we inspect
the user instruction that triggered the trap. However this may sleep
if the page needs to be faulted in (get_user_instr() reaches
__get_user(), which calls might_fault() and triggers the bug message).
Move the HASHCHK handler logic to after we allow IRQs, which is fine
because we are only interested in HASHCHK if it's a user space trap.
Fixes: 5bcba4e6c13f ("powerpc/dexcr: Handle hashchk exception")
Signed-off-by: Benjamin Gray <bg...@linux.ibm.com>
---
v1: https://lore.kernel.org/all/20230825014910.488822-1-bg...@linux.ibm.com/
v1 -> v2: Changed commit description to mention Syzkaller and bug output
---
arch/powerpc/kernel/traps.c | 56 ++++++++++++++++++++++++-------------
1 file changed, 36 insertions(+), 20 deletions(-)
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index eeff136b83d9..64ff37721fd0 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1512,23 +1512,11 @@ static void do_program_check(struct pt_regs *regs)
return;
}
- if (cpu_has_feature(CPU_FTR_DEXCR_NPHIE) && user_mode(regs)) {
- ppc_inst_t insn;
-
- if (get_user_instr(insn, (void __user *)regs->nip)) {
- _exception(SIGSEGV, regs, SEGV_MAPERR,
regs->nip);
- return;
- }
-
- if (ppc_inst_primary_opcode(insn) == 31 &&
- get_xop(ppc_inst_val(insn)) == OP_31_XOP_HASHCHK) {
- _exception(SIGILL, regs, ILL_ILLOPN, regs->nip);
- return;
- }
+ /* User mode considers other cases after enabling IRQs */
+ if (!user_mode(regs)) {
+ _exception(SIGTRAP, regs, TRAP_BRKPT, regs->nip);
+ return;
}
-
- _exception(SIGTRAP, regs, TRAP_BRKPT, regs->nip);
- return;
}
#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
if (reason & REASON_TM) {
@@ -1561,16 +1549,44 @@ static void do_program_check(struct pt_regs *regs)
/*
* If we took the program check in the kernel skip down to sending a
- * SIGILL. The subsequent cases all relate to emulating instructions
- * which we should only do for userspace. We also do not want to enable
- * interrupts for kernel faults because that might lead to further
- * faults, and loose the context of the original exception.
+ * SIGILL. The subsequent cases all relate to user space, such as
+ * emulating instructions which we should only do for user space. We
+ * also do not want to enable interrupts for kernel faults because that
+ * might lead to further faults, and loose the context of the original
+ * exception.
*/
if (!user_mode(regs))
goto sigill;
interrupt_cond_local_irq_enable(regs);
+ /*
+ * (reason & REASON_TRAP) is mostly handled before enabling IRQs,
+ * except get_user_instr() can sleep so we cannot reliably inspect the
+ * current instruction in that context. Now that we know we are
+ * handling a user space trap and can sleep, we can check if the trap
+ * was a hashchk failure.
+ */
+ if (reason & REASON_TRAP) {
+ if (cpu_has_feature(CPU_FTR_DEXCR_NPHIE)) {
+ ppc_inst_t insn;
+
+ if (get_user_instr(insn, (void __user *)regs->nip)) {
+ _exception(SIGSEGV, regs, SEGV_MAPERR,
regs->nip);
+ return;
+ }
+
+ if (ppc_inst_primary_opcode(insn) == 31 &&
+ get_xop(ppc_inst_val(insn)) == OP_31_XOP_HASHCHK) {
+ _exception(SIGILL, regs, ILL_ILLOPN, regs->nip);
+ return;
+ }
+ }
+
+ _exception(SIGTRAP, regs, TRAP_BRKPT, regs->nip);
+ return;
+ }
+
/* (reason & REASON_ILLEGAL) would be the obvious thing here,
* but there seems to be a hardware bug on the 405GP (RevD)
* that means ESR is sometimes set incorrectly - either to
--
2.41.0
