From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Martin Subject: Re: [PATCH v2 11/12] arm64: BTI: Reset BTYPE when skipping emulated instructions Date: Fri, 11 Oct 2019 15:47:43 +0100 Message-ID: <20191011144743.GJ27757@arm.com> References: <1570733080-21015-1-git-send-email-Dave.Martin@arm.com> <1570733080-21015-12-git-send-email-Dave.Martin@arm.com> <20191011142157.GC33537@lakrids.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20191011142157.GC33537@lakrids.cambridge.arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Mark Rutland Cc: Paul Elliott , Peter Zijlstra , Catalin Marinas , Will Deacon , Yu-cheng Yu , Amit Kachhap , Vincenzo Frascino , linux-arch@vger.kernel.org, Eugene Syromiatnikov , Szabolcs Nagy , "H.J. Lu" , Andrew Jones , Kees Cook , Arnd Bergmann , Jann Horn , Richard Henderson , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Mark Brown , Thomas Gleixner , linux-arm-kernel@lists.infradead.or List-Id: linux-arch.vger.kernel.org On Fri, Oct 11, 2019 at 03:21:58PM +0100, Mark Rutland wrote: > On Thu, Oct 10, 2019 at 07:44:39PM +0100, Dave Martin wrote: > > Since normal execution of any non-branch instruction resets the > > PSTATE BTYPE field to 0, so do the same thing when emulating a > > trapped instruction. > > > > Branches don't trap directly, so we should never need to assign a > > non-zero value to BTYPE here. > > > > Signed-off-by: Dave Martin > > --- > > arch/arm64/kernel/traps.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c > > index 3af2768..4d8ce50 100644 > > --- a/arch/arm64/kernel/traps.c > > +++ b/arch/arm64/kernel/traps.c > > @@ -331,6 +331,8 @@ void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size) > > > > if (regs->pstate & PSR_MODE32_BIT) > > advance_itstate(regs); > > + else > > + regs->pstate &= ~(u64)PSR_BTYPE_MASK; > > This looks good to me, with one nit below. > > We don't (currently) need the u64 cast here, and it's inconsistent with > what we do elsewhere. If the upper 32-bit of pstate get allocated, we'll > need to fix up all the other masking we do: Huh, looks like I missed that. Dang. Will fix. > [mark@lakrids:~/src/linux]% git grep 'pstate &= ~' > arch/arm64/kernel/armv8_deprecated.c: regs->pstate &= ~PSR_AA32_E_BIT; > arch/arm64/kernel/cpufeature.c: regs->pstate &= ~PSR_SSBS_BIT; > arch/arm64/kernel/debug-monitors.c: regs->pstate &= ~DBG_SPSR_SS; > arch/arm64/kernel/insn.c: pstate &= ~(pstate >> 1); /* PSR_C_BIT &= ~PSR_Z_BIT */ > arch/arm64/kernel/insn.c: pstate &= ~(pstate >> 1); /* PSR_C_BIT &= ~PSR_Z_BIT */ > arch/arm64/kernel/probes/kprobes.c: regs->pstate &= ~PSR_D_BIT; > arch/arm64/kernel/probes/kprobes.c: regs->pstate &= ~DAIF_MASK; > arch/arm64/kernel/ptrace.c: regs->pstate &= ~SPSR_EL1_AARCH32_RES0_BITS; > arch/arm64/kernel/ptrace.c: regs->pstate &= ~PSR_AA32_E_BIT; > arch/arm64/kernel/ptrace.c: regs->pstate &= ~SPSR_EL1_AARCH64_RES0_BITS; > arch/arm64/kernel/ptrace.c: regs->pstate &= ~DBG_SPSR_SS; > arch/arm64/kernel/ssbd.c: task_pt_regs(task)->pstate &= ~val; > arch/arm64/kernel/traps.c: regs->pstate &= ~PSR_AA32_IT_MASK; > > ... and at that point I'd suggest we should just ensure the bit > definitions are all defined as unsigned long in the first place since > adding casts to each use is error-prone. Are we concerned about changing the types of UAPI #defines? That can cause subtle and unexpected breakage, especially when the signedness of a #define changes. Ideally, we'd just change all these to 1UL << n. Cheers ---Dave From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.110.172]:34710 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726174AbfJKOrt (ORCPT ); Fri, 11 Oct 2019 10:47:49 -0400 Date: Fri, 11 Oct 2019 15:47:43 +0100 From: Dave Martin Subject: Re: [PATCH v2 11/12] arm64: BTI: Reset BTYPE when skipping emulated instructions Message-ID: <20191011144743.GJ27757@arm.com> References: <1570733080-21015-1-git-send-email-Dave.Martin@arm.com> <1570733080-21015-12-git-send-email-Dave.Martin@arm.com> <20191011142157.GC33537@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191011142157.GC33537@lakrids.cambridge.arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Mark Rutland Cc: Paul Elliott , Peter Zijlstra , Catalin Marinas , Will Deacon , Yu-cheng Yu , Amit Kachhap , Vincenzo Frascino , linux-arch@vger.kernel.org, Eugene Syromiatnikov , Szabolcs Nagy , "H.J. Lu" , Andrew Jones , Kees Cook , Arnd Bergmann , Jann Horn , Richard Henderson , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Mark Brown , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Florian Weimer , linux-kernel@vger.kernel.org, Sudakshina Das Message-ID: <20191011144743.0NjB9gxoSeq4Tp5Y6twpfCoBjRtjJ0bQ5ZqKFpa2A0E@z> On Fri, Oct 11, 2019 at 03:21:58PM +0100, Mark Rutland wrote: > On Thu, Oct 10, 2019 at 07:44:39PM +0100, Dave Martin wrote: > > Since normal execution of any non-branch instruction resets the > > PSTATE BTYPE field to 0, so do the same thing when emulating a > > trapped instruction. > > > > Branches don't trap directly, so we should never need to assign a > > non-zero value to BTYPE here. > > > > Signed-off-by: Dave Martin > > --- > > arch/arm64/kernel/traps.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c > > index 3af2768..4d8ce50 100644 > > --- a/arch/arm64/kernel/traps.c > > +++ b/arch/arm64/kernel/traps.c > > @@ -331,6 +331,8 @@ void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size) > > > > if (regs->pstate & PSR_MODE32_BIT) > > advance_itstate(regs); > > + else > > + regs->pstate &= ~(u64)PSR_BTYPE_MASK; > > This looks good to me, with one nit below. > > We don't (currently) need the u64 cast here, and it's inconsistent with > what we do elsewhere. If the upper 32-bit of pstate get allocated, we'll > need to fix up all the other masking we do: Huh, looks like I missed that. Dang. Will fix. > [mark@lakrids:~/src/linux]% git grep 'pstate &= ~' > arch/arm64/kernel/armv8_deprecated.c: regs->pstate &= ~PSR_AA32_E_BIT; > arch/arm64/kernel/cpufeature.c: regs->pstate &= ~PSR_SSBS_BIT; > arch/arm64/kernel/debug-monitors.c: regs->pstate &= ~DBG_SPSR_SS; > arch/arm64/kernel/insn.c: pstate &= ~(pstate >> 1); /* PSR_C_BIT &= ~PSR_Z_BIT */ > arch/arm64/kernel/insn.c: pstate &= ~(pstate >> 1); /* PSR_C_BIT &= ~PSR_Z_BIT */ > arch/arm64/kernel/probes/kprobes.c: regs->pstate &= ~PSR_D_BIT; > arch/arm64/kernel/probes/kprobes.c: regs->pstate &= ~DAIF_MASK; > arch/arm64/kernel/ptrace.c: regs->pstate &= ~SPSR_EL1_AARCH32_RES0_BITS; > arch/arm64/kernel/ptrace.c: regs->pstate &= ~PSR_AA32_E_BIT; > arch/arm64/kernel/ptrace.c: regs->pstate &= ~SPSR_EL1_AARCH64_RES0_BITS; > arch/arm64/kernel/ptrace.c: regs->pstate &= ~DBG_SPSR_SS; > arch/arm64/kernel/ssbd.c: task_pt_regs(task)->pstate &= ~val; > arch/arm64/kernel/traps.c: regs->pstate &= ~PSR_AA32_IT_MASK; > > ... and at that point I'd suggest we should just ensure the bit > definitions are all defined as unsigned long in the first place since > adding casts to each use is error-prone. Are we concerned about changing the types of UAPI #defines? That can cause subtle and unexpected breakage, especially when the signedness of a #define changes. Ideally, we'd just change all these to 1UL << n. Cheers ---Dave