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Wed, 20 Aug 2025 14:38:50 -0700 (PDT) Received: from krava ([176.74.159.170]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-afded47933dsm253096366b.65.2025.08.20.14.38.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 Aug 2025 14:38:50 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Wed, 20 Aug 2025 23:38:48 +0200 To: Peter Zijlstra Cc: Oleg Nesterov , Andrii Nakryiko , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org, Song Liu , Yonghong Song , John Fastabend , Hao Luo , Steven Rostedt , Masami Hiramatsu , Alan Maguire , David Laight , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Ingo Molnar , rick.p.edgecombe@intel.com Subject: Re: [PATCHv6 perf/core 10/22] uprobes/x86: Add support to optimize uprobes Message-ID: References: <20250720112133.244369-1-jolsa@kernel.org> <20250720112133.244369-11-jolsa@kernel.org> <20250819191515.GM3289052@noisy.programming.kicks-ass.net> <20250820123033.GL3245006@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250820123033.GL3245006@noisy.programming.kicks-ass.net> On Wed, Aug 20, 2025 at 02:30:33PM +0200, Peter Zijlstra wrote: > On Tue, Aug 19, 2025 at 09:15:15PM +0200, Peter Zijlstra wrote: > > On Sun, Jul 20, 2025 at 01:21:20PM +0200, Jiri Olsa wrote: > > > > +void arch_uprobe_optimize(struct arch_uprobe *auprobe, unsigned long vaddr) > > > +{ > > > + struct mm_struct *mm = current->mm; > > > + uprobe_opcode_t insn[5]; > > > + > > > + /* > > > + * Do not optimize if shadow stack is enabled, the return address hijack > > > + * code in arch_uretprobe_hijack_return_addr updates wrong frame when > > > + * the entry uprobe is optimized and the shadow stack crashes the app. > > > + */ > > > + if (shstk_is_enabled()) > > > + return; > > > > Kernel should be able to fix up userspace shadow stack just fine. > > > > > + if (!should_optimize(auprobe)) > > > + return; > > > + > > > + mmap_write_lock(mm); > > > + > > > + /* > > > + * Check if some other thread already optimized the uprobe for us, > > > + * if it's the case just go away silently. > > > + */ > > > + if (copy_from_vaddr(mm, vaddr, &insn, 5)) > > > + goto unlock; > > > + if (!is_swbp_insn((uprobe_opcode_t*) &insn)) > > > + goto unlock; > > > + > > > + /* > > > + * If we fail to optimize the uprobe we set the fail bit so the > > > + * above should_optimize will fail from now on. > > > + */ > > > + if (__arch_uprobe_optimize(auprobe, mm, vaddr)) > > > + set_bit(ARCH_UPROBE_FLAG_OPTIMIZE_FAIL, &auprobe->flags); > > > + > > > +unlock: > > > + mmap_write_unlock(mm); > > > +} > > Something a little like this should do I suppose... > > --- a/arch/x86/include/asm/shstk.h > +++ b/arch/x86/include/asm/shstk.h > @@ -23,6 +23,8 @@ int setup_signal_shadow_stack(struct ksi > int restore_signal_shadow_stack(void); > int shstk_update_last_frame(unsigned long val); > bool shstk_is_enabled(void); > +int shstk_pop(u64 *val); > +int shstk_push(u64 val); > #else > static inline long shstk_prctl(struct task_struct *task, int option, > unsigned long arg2) { return -EINVAL; } > @@ -35,6 +37,8 @@ static inline int setup_signal_shadow_st > static inline int restore_signal_shadow_stack(void) { return 0; } > static inline int shstk_update_last_frame(unsigned long val) { return 0; } > static inline bool shstk_is_enabled(void) { return false; } > +static inline int shstk_pop(u64 *val) { return -ENOTSUPP; } > +static inline int shstk_push(u64 val) { return -ENOTSUPP; } > #endif /* CONFIG_X86_USER_SHADOW_STACK */ > > #endif /* __ASSEMBLER__ */ > --- a/arch/x86/kernel/shstk.c > +++ b/arch/x86/kernel/shstk.c > @@ -246,6 +246,46 @@ static unsigned long get_user_shstk_addr > return ssp; > } > > +int shstk_pop(u64 *val) > +{ > + int ret = 0; > + u64 ssp; > + > + if (!features_enabled(ARCH_SHSTK_SHSTK)) > + return -ENOTSUPP; > + > + fpregs_lock_and_load(); > + > + rdmsrq(MSR_IA32_PL3_SSP, ssp); > + if (val && get_user(*val, (__user u64 *)ssp)) > + ret = -EFAULT; > + ssp += SS_FRAME_SIZE; > + wrmsrq(MSR_IA32_PL3_SSP, ssp); > + > + fpregs_unlock(); > + > + return ret; > +} > + > +int shstk_push(u64 val) > +{ > + u64 ssp; > + int ret; > + > + if (!features_enabled(ARCH_SHSTK_SHSTK)) > + return -ENOTSUPP; > + > + fpregs_lock_and_load(); > + > + rdmsrq(MSR_IA32_PL3_SSP, ssp); > + ssp -= SS_FRAME_SIZE; > + wrmsrq(MSR_IA32_PL3_SSP, ssp); > + ret = write_user_shstk_64((__user void *)ssp, val); > + fpregs_unlock(); > + > + return ret; > +} > + > #define SHSTK_DATA_BIT BIT(63) > > static int put_shstk_data(u64 __user *addr, u64 data) > --- a/arch/x86/kernel/uprobes.c > +++ b/arch/x86/kernel/uprobes.c > @@ -804,7 +804,7 @@ SYSCALL_DEFINE0(uprobe) > { > struct pt_regs *regs = task_pt_regs(current); > struct uprobe_syscall_args args; > - unsigned long ip, sp; > + unsigned long ip, sp, sret; > int err; > > /* Allow execution only from uprobe trampolines. */ > @@ -831,6 +831,9 @@ SYSCALL_DEFINE0(uprobe) > > sp = regs->sp; > > + if (shstk_pop(&sret) == 0 && sret != args.retaddr) > + goto sigill; > + > handle_syscall_uprobe(regs, regs->ip); > > /* > @@ -855,6 +858,9 @@ SYSCALL_DEFINE0(uprobe) > if (args.retaddr - 5 != regs->ip) > args.retaddr = regs->ip; > > + if (shstk_push(args.retaddr) == -EFAULT) > + goto sigill; > + > regs->ip = ip; > > err = copy_to_user((void __user *)regs->sp, &args, sizeof(args)); > @@ -1124,14 +1130,6 @@ void arch_uprobe_optimize(struct arch_up > struct mm_struct *mm = current->mm; > uprobe_opcode_t insn[5]; > > - /* > - * Do not optimize if shadow stack is enabled, the return address hijack > - * code in arch_uretprobe_hijack_return_addr updates wrong frame when > - * the entry uprobe is optimized and the shadow stack crashes the app. > - */ > - if (shstk_is_enabled()) > - return; > - nice, we will need to adjust selftests for that, there's shadow stack part in prog_tests/uprobe_syscall.c that expects non optimized uprobe after enabling shadow stack.. I'll run it and send the change thanks, jirka