From: Nicholas Piggin npiggin@gmail.com
commit b871895b148256f1721bc565d803860242755a0b upstream.
If a system call is made with a transaction active, the kernel immediately aborts it and returns. scv system calls disable irqs even earlier in their interrupt handler, and tabort_syscall does not fix this up.
This can result in irq soft-mask state being messed up on the next kernel entry, and crashing at BUG_ON(arch_irq_disabled_regs(regs)) in the kernel exit handlers, or possibly worse.
This can't easily be fixed in asm because at this point an async irq may have hit, which is soft-masked and marked pending. The pending interrupt has to be replayed before returning to userspace. The fix is to move the tabort_syscall code to C in the main syscall handler, and just skip the system call but otherwise return as usual, which will take care of the pending irqs. This also does a bunch of other things including possible signal delivery to the process, but the doomed transaction should still be aborted when it is eventually returned to.
The sc system call path is changed to use the new C function as well to reduce code and path differences. This slows down how quickly system calls are aborted when called while a transaction is active, which could potentially impact TM performance. But making any system call is already bad for performance, and TM is on the way out, so go with simpler over faster.
Fixes: 7fa95f9adaee7 ("powerpc/64s: system call support for scv/rfscv instructions") Reported-by: Eirik Fuller efuller@redhat.com Signed-off-by: Nicholas Piggin npiggin@gmail.com [mpe: Use #ifdef rather than IS_ENABLED() to fix build error on 32-bit] Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20210903125707.1601269-1-npiggin@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/kernel/interrupt.c | 30 +++++++++++++++++++++++++++ arch/powerpc/kernel/interrupt_64.S | 41 ------------------------------------- 2 files changed, 30 insertions(+), 41 deletions(-)
--- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c @@ -19,6 +19,7 @@ #include <asm/switch_to.h> #include <asm/syscall.h> #include <asm/time.h> +#include <asm/tm.h> #include <asm/unistd.h>
#if defined(CONFIG_PPC_ADV_DEBUG_REGS) && defined(CONFIG_PPC32) @@ -138,6 +139,35 @@ notrace long system_call_exception(long */ irq_soft_mask_regs_set_state(regs, IRQS_ENABLED);
+ /* + * If the system call was made with a transaction active, doom it and + * return without performing the system call. Unless it was an + * unsupported scv vector, in which case it's treated like an illegal + * instruction. + */ +#ifdef CONFIG_PPC_TRANSACTIONAL_MEM + if (unlikely(MSR_TM_TRANSACTIONAL(regs->msr)) && + !trap_is_unsupported_scv(regs)) { + /* Enable TM in the kernel, and disable EE (for scv) */ + hard_irq_disable(); + mtmsr(mfmsr() | MSR_TM); + + /* tabort, this dooms the transaction, nothing else */ + asm volatile(".long 0x7c00071d | ((%0) << 16)" + :: "r"(TM_CAUSE_SYSCALL|TM_CAUSE_PERSISTENT)); + + /* + * Userspace will never see the return value. Execution will + * resume after the tbegin. of the aborted transaction with the + * checkpointed register state. A context switch could occur + * or signal delivered to the process before resuming the + * doomed transaction context, but that should all be handled + * as expected. + */ + return -ENOSYS; + } +#endif // CONFIG_PPC_TRANSACTIONAL_MEM + local_irq_enable();
if (unlikely(current_thread_info()->flags & _TIF_SYSCALL_DOTRACE)) { --- a/arch/powerpc/kernel/interrupt_64.S +++ b/arch/powerpc/kernel/interrupt_64.S @@ -12,7 +12,6 @@ #include <asm/mmu.h> #include <asm/ppc_asm.h> #include <asm/ptrace.h> -#include <asm/tm.h>
.section ".toc","aw" SYS_CALL_TABLE: @@ -55,12 +54,6 @@ COMPAT_SYS_CALL_TABLE: .globl system_call_vectored_\name system_call_vectored_\name: _ASM_NOKPROBE_SYMBOL(system_call_vectored_\name) -#ifdef CONFIG_PPC_TRANSACTIONAL_MEM -BEGIN_FTR_SECTION - extrdi. r10, r12, 1, (63-MSR_TS_T_LG) /* transaction active? */ - bne tabort_syscall -END_FTR_SECTION_IFSET(CPU_FTR_TM) -#endif SCV_INTERRUPT_TO_KERNEL mr r10,r1 ld r1,PACAKSAVE(r13) @@ -247,12 +240,6 @@ _ASM_NOKPROBE_SYMBOL(system_call_common_ .globl system_call_common system_call_common: _ASM_NOKPROBE_SYMBOL(system_call_common) -#ifdef CONFIG_PPC_TRANSACTIONAL_MEM -BEGIN_FTR_SECTION - extrdi. r10, r12, 1, (63-MSR_TS_T_LG) /* transaction active? */ - bne tabort_syscall -END_FTR_SECTION_IFSET(CPU_FTR_TM) -#endif mr r10,r1 ld r1,PACAKSAVE(r13) std r10,0(r1) @@ -425,34 +412,6 @@ SOFT_MASK_TABLE(.Lsyscall_rst_start, 1b) RESTART_TABLE(.Lsyscall_rst_start, .Lsyscall_rst_end, syscall_restart) #endif
-#ifdef CONFIG_PPC_TRANSACTIONAL_MEM -tabort_syscall: -_ASM_NOKPROBE_SYMBOL(tabort_syscall) - /* Firstly we need to enable TM in the kernel */ - mfmsr r10 - li r9, 1 - rldimi r10, r9, MSR_TM_LG, 63-MSR_TM_LG - mtmsrd r10, 0 - - /* tabort, this dooms the transaction, nothing else */ - li r9, (TM_CAUSE_SYSCALL|TM_CAUSE_PERSISTENT) - TABORT(R9) - - /* - * Return directly to userspace. We have corrupted user register state, - * but userspace will never see that register state. Execution will - * resume after the tbegin of the aborted transaction with the - * checkpointed register state. - */ - li r9, MSR_RI - andc r10, r10, r9 - mtmsrd r10, 1 - mtspr SPRN_SRR0, r11 - mtspr SPRN_SRR1, r12 - RFI_TO_USER - b . /* prevent speculative execution */ -#endif - /* * If MSR EE/RI was never enabled, IRQs not reconciled, NVGPRs not * touched, no exit work created, then this can be used.