From patchwork Tue Jul 24 13:17:20 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "H.J. Lu" X-Patchwork-Id: 28584 Received: (qmail 100510 invoked by alias); 24 Jul 2018 13:17:29 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 100460 invoked by uid 89); 24 Jul 2018 13:17:28 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-25.3 required=5.0 tests=AWL, BAYES_00, FREEMAIL_FROM, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, RCVD_IN_DNSWL_NONE, SPF_PASS autolearn=ham version=3.3.2 spammy= X-HELO: mail-oi0-f66.google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=MmbrcaNLfmbPRt0H52FN9JoVt+8v3et0zLqvAIpTZ84=; b=g3+bDMmQV4iaxmK3WEVWBmh2aIPHnHbm2CRRtk3XBTYTmhrlN+FoZM0ls0Q1ZrRnWp ThNlaDaDq7O+G6zbkyNL+Iuc+0K+aZqaU7zZu6XNEzzq5luGahq3/5D6lYfDRTCM1eID bmchvKrLeBpTGihrALu32gU1rkEiwta7fLZsLLZgj1uBMETMX394ym+saiqel/UyE3vJ iCv53QXivpuPUs2M217YBR2RldWsxr/TnnfL4yfLb0T+2VH0yfiXgH3oznWpFmHy4snt DpdowgPrC1rHoanDoirQfT+r5muTRIzvlwOIs4uj6oGKX677tkRNt2c9QM/HcYbIHCqs EQpw== MIME-Version: 1.0 In-Reply-To: <5681eff6-b814-8655-f72d-8e4d77ac5930@redhat.com> References: <20180721142035.21059-1-hjl.tools@gmail.com> <20180721142035.21059-2-hjl.tools@gmail.com> <5681eff6-b814-8655-f72d-8e4d77ac5930@redhat.com> From: "H.J. Lu" Date: Tue, 24 Jul 2018 06:17:20 -0700 Message-ID: Subject: Re: [PATCH 01/12] x86: Update vfork to pop shadow stack To: "Carlos O'Donell" Cc: GNU C Library On Tue, Jul 24, 2018 at 5:32 AM, Carlos O'Donell wrote: > On 07/24/2018 08:25 AM, H.J. Lu wrote: >> On Mon, Jul 23, 2018 at 7:47 PM, Carlos O'Donell wrote: >>> On 07/21/2018 10:20 AM, H.J. Lu wrote: >>>> Since we can't change return address on shadow stack, if shadow stack >>>> is in use, we need to pop shadow stack and jump back to caller directly. >>>> >>>> * sysdeps/unix/sysv/linux/i386/vfork.S (SYSCALL_ERROR_HANDLER): >>>> Redefine if shadow stack is enabled. >>>> (SYSCALL_ERROR_LABEL): Likewise. >>>> (__vfork): Pop shadow stack and jump back to to caller directly >>>> when shadow stack is in use. >>>> * sysdeps/unix/sysv/linux/x86_64/vfork.S (SYSCALL_ERROR_HANDLER): >>>> Redefine if shadow stack is enabled. >>>> (SYSCALL_ERROR_LABEL): Likewise. >>>> (__vfork): Pop shadow stack and jump back to to caller directly >>>> when shadow stack is in use. >>>> --- >>>> sysdeps/unix/sysv/linux/i386/vfork.S | 54 ++++++++++++++++++++++++++ >>>> sysdeps/unix/sysv/linux/x86_64/vfork.S | 35 +++++++++++++++++ >>>> 2 files changed, 89 insertions(+) >>> >>> OK with comment suggestion. >>> >>> Reviewed-by: Carlos O'Donell >>> >> >> This is what I checked in. >> >> Thanks. >> > > Wrong patch? > Oops. Here is the right one. From 3650e1d9284926be67e368707a9a2276fb77a167 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Tue, 24 Jul 2018 05:20:48 -0700 Subject: [PATCH] x86: Update vfork to pop shadow stack The shadow stack prevents us from pushing the saved return PC onto the stack and returning normally. Instead we pop the shadow stack and return directly. This is the safest way to return and ensures any stack manipulations done by the vfork'd child doesn't cause the parent to terminate when CET is enabled. Reviewed-by: Carlos O'Donell * sysdeps/unix/sysv/linux/i386/vfork.S (SYSCALL_ERROR_HANDLER): Redefine if shadow stack is enabled. (SYSCALL_ERROR_LABEL): Likewise. (__vfork): Pop shadow stack and jump back to to caller directly when shadow stack is in use. * sysdeps/unix/sysv/linux/x86_64/vfork.S (SYSCALL_ERROR_HANDLER): Redefine if shadow stack is enabled. (SYSCALL_ERROR_LABEL): Likewise. (__vfork): Pop shadow stack and jump back to to caller directly when shadow stack is in use. --- ChangeLog | 13 ++++++ sysdeps/unix/sysv/linux/i386/vfork.S | 57 ++++++++++++++++++++++++++ sysdeps/unix/sysv/linux/x86_64/vfork.S | 38 +++++++++++++++++ 3 files changed, 108 insertions(+) diff --git a/ChangeLog b/ChangeLog index 2a1a53d9df..8b892eb686 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,16 @@ +2018-07-24 H.J. Lu + + * sysdeps/unix/sysv/linux/i386/vfork.S (SYSCALL_ERROR_HANDLER): + Redefine if shadow stack is enabled. + (SYSCALL_ERROR_LABEL): Likewise. + (__vfork): Pop shadow stack and jump back to to caller directly + when shadow stack is in use. + * sysdeps/unix/sysv/linux/x86_64/vfork.S (SYSCALL_ERROR_HANDLER): + Redefine if shadow stack is enabled. + (SYSCALL_ERROR_LABEL): Likewise. + (__vfork): Pop shadow stack and jump back to to caller directly + when shadow stack is in use. + 2018-07-24 H.J. Lu * sysdeps/x86_64/tst-quadmod1.S (func): Add endbr64 if IBT is diff --git a/sysdeps/unix/sysv/linux/i386/vfork.S b/sysdeps/unix/sysv/linux/i386/vfork.S index 8f40d02d09..ce6dbfac48 100644 --- a/sysdeps/unix/sysv/linux/i386/vfork.S +++ b/sysdeps/unix/sysv/linux/i386/vfork.S @@ -21,6 +21,38 @@ #include #include +#if SHSTK_ENABLED +/* The shadow stack prevents us from pushing the saved return PC onto + the stack and returning normally. Instead we pop the shadow stack + and return directly. This is the safest way to return and ensures + any stack manipulations done by the vfork'd child doesn't cause the + parent to terminate when CET is enabled. */ +# undef SYSCALL_ERROR_HANDLER +# ifdef PIC +# define SYSCALL_ERROR_HANDLER \ +0: \ + calll .L1; \ +.L1: \ + popl %edx; \ +.L2: \ + addl $_GLOBAL_OFFSET_TABLE_ + (.L2 - .L1), %edx; \ + movl __libc_errno@gotntpoff(%edx), %edx; \ + negl %eax; \ + movl %eax, %gs:(%edx); \ + orl $-1, %eax; \ + jmp 1b; +# else +# define SYSCALL_ERROR_HANDLER \ +0: \ + movl __libc_errno@indntpoff, %edx; \ + negl %eax; \ + movl %eax, %gs:(%edx); \ + orl $-1, %eax; \ + jmp 1b; +# endif +# undef SYSCALL_ERROR_LABEL +# define SYSCALL_ERROR_LABEL 0f +#endif /* Clone the calling process, but without copying the whole address space. The calling process is suspended until the new process exits or is @@ -38,16 +70,41 @@ ENTRY (__vfork) movl $SYS_ify (vfork), %eax int $0x80 +#if !SHSTK_ENABLED /* Jump to the return PC. Don't jump directly since this disturbs the branch target cache. Instead push the return address back on the stack. */ pushl %ecx cfi_adjust_cfa_offset (4) +#endif cmpl $-4095, %eax /* Branch forward if it failed. */ jae SYSCALL_ERROR_LABEL +#if SHSTK_ENABLED +1: + /* Check if shadow stack is in use. */ + xorl %edx, %edx + rdsspd %edx + testl %edx, %edx + /* Normal return if shadow stack isn't in use. */ + je L(no_shstk) + + /* Pop return address from shadow stack and jump back to caller + directly. */ + movl $1, %edx + incsspd %edx + jmp *%ecx + +L(no_shstk): + /* Jump to the return PC. Don't jump directly since this + disturbs the branch target cache. Instead push the return + address back on the stack. */ + pushl %ecx + cfi_adjust_cfa_offset (4) +#endif + ret PSEUDO_END (__vfork) diff --git a/sysdeps/unix/sysv/linux/x86_64/vfork.S b/sysdeps/unix/sysv/linux/x86_64/vfork.S index e4c8269e3d..8f1ca9f836 100644 --- a/sysdeps/unix/sysv/linux/x86_64/vfork.S +++ b/sysdeps/unix/sysv/linux/x86_64/vfork.S @@ -20,6 +20,21 @@ #include #include +#if SHSTK_ENABLED +/* The shadow stack prevents us from pushing the saved return PC onto + the stack and returning normally. Instead we pop the shadow stack + and return directly. This is the safest way to return and ensures + any stack manipulations done by the vfork'd child doesn't cause the + parent to terminate when CET is enabled. */ +# undef SYSCALL_ERROR_HANDLER +# define SYSCALL_ERROR_HANDLER \ +0: \ + SYSCALL_SET_ERRNO; \ + or $-1, %RAX_LP; \ + jmp 1b; +# undef SYSCALL_ERROR_LABEL +# define SYSCALL_ERROR_LABEL 0f +#endif /* Clone the calling process, but without copying the whole address space. The calling process is suspended until the new process exits or is @@ -38,13 +53,36 @@ ENTRY (__vfork) movl $SYS_ify (vfork), %eax syscall +#if !SHSTK_ENABLED /* Push back the return PC. */ pushq %rdi cfi_adjust_cfa_offset(8) +#endif cmpl $-4095, %eax jae SYSCALL_ERROR_LABEL /* Branch forward if it failed. */ +#if SHSTK_ENABLED +1: + /* Check if shadow stack is in use. */ + xorl %esi, %esi + rdsspq %rsi + testq %rsi, %rsi + /* Normal return if shadow stack isn't in use. */ + je L(no_shstk) + + /* Pop return address from shadow stack and jump back to caller + directly. */ + movl $1, %esi + incsspq %rsi + jmp *%rdi + +L(no_shstk): + /* Push back the return PC. */ + pushq %rdi + cfi_adjust_cfa_offset(8) +#endif + /* Normal return. */ ret -- 2.17.1