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Message-ID: <87976f9b-2c36-b4f7-5382-4eba569cc687@oracle.com>
Date: Thu, 7 May 2020 15:39:20 +0200
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: Thomas Gleixner <tglx@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>
Cc: x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
Andy Lutomirski <luto@...nel.org>,
Frederic Weisbecker <frederic@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Petr Mladek <pmladek@...e.com>,
Steven Rostedt <rostedt@...dmis.org>,
Joel Fernandes <joel@...lfernandes.org>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Juergen Gross <jgross@...e.com>,
Brian Gerst <brgerst@...il.com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 2 04/18] x86/entry/common: Protect against
instrumentation
On 5/5/20 3:41 PM, Thomas Gleixner wrote:
> Mark the various syscall entries with noinstr to protect them against
> instrumentation and add the noinstr_begin()/end() annotations to mark the
> parts of the functions which are safe to call out into instrumentable code.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
> arch/x86/entry/common.c | 135 ++++++++++++++++++++++++++++++++----------------
> 1 file changed, 90 insertions(+), 45 deletions(-)
>
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -41,15 +41,26 @@
>
> #ifdef CONFIG_CONTEXT_TRACKING
> /* Called on entry from user mode with IRQs off. */
> -__visible inline noinstr void enter_from_user_mode(void)
> +__visible noinstr void enter_from_user_mode(void)
> {
> - CT_WARN_ON(ct_state() != CONTEXT_USER);
> + enum ctx_state state = ct_state();
> +
> user_exit_irqoff();
> +
> + instr_begin();
> + CT_WARN_ON(state != CONTEXT_USER);
> + instr_end();
> }
> #else
> static inline void enter_from_user_mode(void) {}
> #endif
>
> +static noinstr void exit_to_user_mode(void)
> +{
> + user_enter_irqoff();
> + mds_user_clear_cpu_buffers();
> +}
> +
> static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
> {
> #ifdef CONFIG_X86_64
> @@ -179,8 +190,7 @@ static void exit_to_usermode_loop(struct
> }
> }
>
> -/* Called with IRQs disabled. */
> -__visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
> +static void __prepare_exit_to_usermode(struct pt_regs *regs)
> {
> struct thread_info *ti = current_thread_info();
> u32 cached_flags;
> @@ -219,10 +229,14 @@ static void exit_to_usermode_loop(struct
> */
> ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED);
> #endif
> +}
>
> - user_enter_irqoff();
> -
> - mds_user_clear_cpu_buffers();
> +__visible noinstr void prepare_exit_to_usermode(struct pt_regs *regs)
> +{
> + instr_begin();
> + __prepare_exit_to_usermode(regs);
> + instr_end();
> + exit_to_user_mode();
> }
>
> #define SYSCALL_EXIT_WORK_FLAGS \
> @@ -251,11 +265,7 @@ static void syscall_slow_exit_work(struc
> tracehook_report_syscall_exit(regs, step);
> }
>
> -/*
> - * Called with IRQs on and fully valid regs. Returns with IRQs off in a
> - * state such that we can immediately switch to user mode.
> - */
> -__visible inline void syscall_return_slowpath(struct pt_regs *regs)
> +static void __syscall_return_slowpath(struct pt_regs *regs)
> {
> struct thread_info *ti = current_thread_info();
> u32 cached_flags = READ_ONCE(ti->flags);
> @@ -276,15 +286,29 @@ static void syscall_slow_exit_work(struc
> syscall_slow_exit_work(regs, cached_flags);
>
> local_irq_disable();
> - prepare_exit_to_usermode(regs);
> + __prepare_exit_to_usermode(regs);
> +}
> +
> +/*
> + * Called with IRQs on and fully valid regs. Returns with IRQs off in a
> + * state such that we can immediately switch to user mode.
> + */
> +__visible noinstr void syscall_return_slowpath(struct pt_regs *regs)
> +{
> + instr_begin();
> + __syscall_return_slowpath(regs);
> + instr_end();
> + exit_to_user_mode();
> }
>
> #ifdef CONFIG_X86_64
> -__visible void do_syscall_64(unsigned long nr, struct pt_regs *regs)
> +__visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)
> {
> struct thread_info *ti;
>
> enter_from_user_mode();
> + instr_begin();
> +
> local_irq_enable();
> ti = current_thread_info();
> if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
> @@ -301,8 +325,10 @@ static void syscall_slow_exit_work(struc
> regs->ax = x32_sys_call_table[nr](regs);
> #endif
> }
> + __syscall_return_slowpath(regs);
>
> - syscall_return_slowpath(regs);
> + instr_end();
> + exit_to_user_mode();
> }
> #endif
>
> @@ -310,10 +336,10 @@ static void syscall_slow_exit_work(struc
> /*
> * Does a 32-bit syscall. Called with IRQs on in CONTEXT_KERNEL. Does
> * all entry and exit work and returns with IRQs off. This function is
> - * extremely hot in workloads that use it, and it's usually called from
> + * ex2tremely hot in workloads that use it, and it's usually called from
typo: "ex2tremely"
alex.
> * do_fast_syscall_32, so forcibly inline it to improve performance.
> */
> -static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
> +static void do_syscall_32_irqs_on(struct pt_regs *regs)
> {
> struct thread_info *ti = current_thread_info();
> unsigned int nr = (unsigned int)regs->orig_ax;
> @@ -337,27 +363,62 @@ static __always_inline void do_syscall_3
> regs->ax = ia32_sys_call_table[nr](regs);
> }
>
> - syscall_return_slowpath(regs);
> + __syscall_return_slowpath(regs);
> }
>
> /* Handles int $0x80 */
> -__visible void do_int80_syscall_32(struct pt_regs *regs)
> +__visible noinstr void do_int80_syscall_32(struct pt_regs *regs)
> {
> enter_from_user_mode();
> + instr_begin();
> +
> local_irq_enable();
> do_syscall_32_irqs_on(regs);
> +
> + instr_end();
> + exit_to_user_mode();
> +}
> +
> +static bool __do_fast_syscall_32(struct pt_regs *regs)
> +{
> + int res;
> +
> + /* Fetch EBP from where the vDSO stashed it. */
> + if (IS_ENABLED(CONFIG_X86_64)) {
> + /*
> + * Micro-optimization: the pointer we're following is
> + * explicitly 32 bits, so it can't be out of range.
> + */
> + res = __get_user(*(u32 *)®s->bp,
> + (u32 __user __force *)(unsigned long)(u32)regs->sp);
> + } else {
> + res = get_user(*(u32 *)®s->bp,
> + (u32 __user __force *)(unsigned long)(u32)regs->sp);
> + }
> +
> + if (res) {
> + /* User code screwed up. */
> + regs->ax = -EFAULT;
> + local_irq_disable();
> + __prepare_exit_to_usermode(regs);
> + return false;
> + }
> +
> + /* Now this is just like a normal syscall. */
> + do_syscall_32_irqs_on(regs);
> + return true;
> }
>
> /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
> -__visible long do_fast_syscall_32(struct pt_regs *regs)
> +__visible noinstr long do_fast_syscall_32(struct pt_regs *regs)
> {
> /*
> * Called using the internal vDSO SYSENTER/SYSCALL32 calling
> * convention. Adjust regs so it looks like we entered using int80.
> */
> -
> unsigned long landing_pad = (unsigned long)current->mm->context.vdso +
> - vdso_image_32.sym_int80_landing_pad;
> + vdso_image_32.sym_int80_landing_pad;
> + bool success;
>
> /*
> * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
> @@ -367,33 +428,17 @@ static __always_inline void do_syscall_3
> regs->ip = landing_pad;
>
> enter_from_user_mode();
> + instr_begin();
>
> local_irq_enable();
> + success = __do_fast_syscall_32(regs);
>
> - /* Fetch EBP from where the vDSO stashed it. */
> - if (
> -#ifdef CONFIG_X86_64
> - /*
> - * Micro-optimization: the pointer we're following is explicitly
> - * 32 bits, so it can't be out of range.
> - */
> - __get_user(*(u32 *)®s->bp,
> - (u32 __user __force *)(unsigned long)(u32)regs->sp)
> -#else
> - get_user(*(u32 *)®s->bp,
> - (u32 __user __force *)(unsigned long)(u32)regs->sp)
> -#endif
> - ) {
> -
> - /* User code screwed up. */
> - local_irq_disable();
> - regs->ax = -EFAULT;
> - prepare_exit_to_usermode(regs);
> - return 0; /* Keep it simple: use IRET. */
> - }
> + instr_end();
> + exit_to_user_mode();
>
> - /* Now this is just like a normal syscall. */
> - do_syscall_32_irqs_on(regs);
> + /* If it failed, keep it simple: use IRET. */
> + if (!success)
> + return 0;
>
> #ifdef CONFIG_X86_64
> /*
>
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