6.5-stable review patch. If anyone has any objections, please let me know.
------------------
From: Benjamin Gray bgray@linux.ibm.com
[ Upstream commit c3f4309693758b13fbb34b3741c2e2801ad28769 ]
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 bgray@linux.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://msgid.link/20230915034604.45393-1-bgray@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 7ef147e2a20d7..109b93874df92 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