From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELuGdRnhlE1bLDlZCW9KxKcD5qdC2xub99rOgUAm9PNFjHPXI7Ri8MYrTRqEITc2tWnAOp11 ARC-Seal: i=1; a=rsa-sha256; t=1520824066; cv=none; d=google.com; s=arc-20160816; b=hcmnut4iLQtM7Vh4TjazaOF8g0kPSuDgfEyppQm7Wp5ubQX1H7j1G2YQNYLKJyGHSh V1WTZgL5xe9LBDwqKBK6yGZmLRbaNaTP3wlnjr7SQgpIaXxG7wybxo2PMvB4RFyARjwy BkIw0Fm/C/xzlnDWyoE6RG1+oL4G2wqM+jqn4bOwNySbTdDnymOR7Kj7aTXMvA45wVXO 507LKjFxy5DjjSl9DOoYS3OP3smCdlcRM4hX8zJBg1KY5/vJ70B3XbM7Q3pPp3fERgmI 2H54JZ444mqmQ66T8sBLhjfJdjNlQ2AEgwAHEmZjF4H64BJyX3Gj9QsDEQXP96VbgSQB Q+DA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=in-reply-to:subject:message-id:date:cc:to:from:mime-version :content-transfer-encoding:content-disposition :arc-authentication-results; bh=93ORTVi7JzyF6DlXQwOYIfzmDNJz/a98SlPJzzqj5oE=; b=cpfv00Jl+DBxpV/keABHz4y6yoqT/8qLJb8MPCdr8iBgGDASd4+GKrP7pi76c6hjEd vs8uoEiw8odKZUcbisd3th4pKrEdU1ox3cDQGibPHdCczdzTa5dxea0FJtYu4ByXrKdK 56P+C3H2a3apQjab2OfMSVah+F6aloiDQL/phVPTeSHRPdG4TY+YYpcSil/nDamb//rc JrrkZtmY2ZoQhnh2akmDc3kU1tukWmTTKrXPVc3JcG29HzwN+G7KZVUXNI8mpHTlAKX0 yea3sspgUDj8MrQDe8AxZT1Ka+YEKd+fb+HWBvlkxKtdFvofN1W8HZMY8gl8nIfIFXgO elAQ== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of ben@decadent.org.uk designates 88.96.1.126 as permitted sender) smtp.mailfrom=ben@decadent.org.uk Authentication-Results: mx.google.com; spf=pass (google.com: domain of ben@decadent.org.uk designates 88.96.1.126 as permitted sender) smtp.mailfrom=ben@decadent.org.uk Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Dan Williams" , "Linus Torvalds" , "Jiri Slaby" , kernel-hardening@lists.openwall.com, alan@linux.intel.com, "Jan Beulich" , linux-arch@vger.kernel.org, "Andy Lutomirski" , "Jinpu Wang" , gregkh@linuxfoundation.org, "Thomas Gleixner" Date: Mon, 12 Mar 2018 03:03:34 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 087/104] x86/syscall: Sanitize syscall table de-references under speculation In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1594699616206088143?= X-GMAIL-MSGID: =?utf-8?q?1594699616206088143?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 3.2.101-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Ben Hutchings commit 2fbd7af5af8665d18bcefae3e9700be07e22b681 upstream. The upstream version of this, touching C code, was written by Dan Williams, with the following description: > The syscall table base is a user controlled function pointer in kernel > space. Use array_index_nospec() to prevent any out of bounds speculation. > > While retpoline prevents speculating into a userspace directed target it > does not stop the pointer de-reference, the concern is leaking memory > relative to the syscall table base, by observing instruction cache > behavior. The x86_64 assembly version for 4.4 was written by Jiri Slaby, with the following description: > In 4.4.118, we have commit c8961332d6da (x86/syscall: Sanitize syscall > table de-references under speculation), which is a backport of upstream > commit 2fbd7af5af86. But it fixed only the C part of the upstream patch > -- the IA32 sysentry. So it ommitted completely the assembly part -- the > 64bit sysentry. > > Fix that in this patch by explicit array_index_mask_nospec written in > assembly. The same was used in lib/getuser.S. > > However, to have "sbb" working properly, we have to switch from "cmp" > against (NR_syscalls-1) to (NR_syscalls), otherwise the last syscall > number would be "and"ed by 0. It is because the original "ja" relies on > "CF" or "ZF", but we rely only on "CF" in "sbb". That means: switch to > "jae" conditional jump too. > > Final note: use rcx for mask as this is exactly what is overwritten by > the 4th syscall argument (r10) right after. In 3.2 the x86_32 syscall table lookup is also written in assembly. So I've taken Jiri's version and added similar masking in entry_32.S, using edx as the temporary. edx is clobbered by SAVE_REGS and seems to be free at this point. In 3.2 the x86_64 entry code also lacks syscall masking for x32. Cc: Dan Williams Cc: Jiri Slaby Cc: Jan Beulich Cc: Linus Torvalds Cc: Thomas Gleixner Cc: linux-arch@vger.kernel.org Cc: kernel-hardening@lists.openwall.com Cc: gregkh@linuxfoundation.org Cc: Andy Lutomirski Cc: alan@linux.intel.com Cc: Jinpu Wang Signed-off-by: Ben Hutchings --- --- a/arch/x86/kernel/entry_32.S +++ b/arch/x86/kernel/entry_32.S @@ -429,6 +429,8 @@ sysenter_past_esp: sysenter_do_call: cmpl $(nr_syscalls), %eax jae sysenter_badsys + sbb %edx, %edx /* array_index_mask_nospec() */ + and %edx, %eax call *sys_call_table(,%eax,4) sysenter_after_call: movl %eax,PT_EAX(%esp) @@ -512,6 +514,8 @@ ENTRY(system_call) cmpl $(nr_syscalls), %eax jae syscall_badsys syscall_call: + sbb %edx, %edx /* array_index_mask_nospec() */ + and %edx, %eax call *sys_call_table(,%eax,4) syscall_after_call: movl %eax,PT_EAX(%esp) # store the return value --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -517,8 +517,10 @@ ENTRY(system_call_after_swapgs) testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%rcx) jnz tracesys system_call_fastpath: - cmpq $__NR_syscall_max,%rax - ja badsys + cmpq $NR_syscalls, %rax + jae badsys + sbb %rcx, %rcx /* array_index_mask_nospec() */ + and %rcx, %rax movq %r10,%rcx #ifdef CONFIG_RETPOLINE movq sys_call_table(, %rax, 8), %rax @@ -646,8 +648,10 @@ tracesys: */ LOAD_ARGS ARGOFFSET, 1 RESTORE_REST - cmpq $__NR_syscall_max,%rax - ja int_ret_from_sys_call /* RAX(%rsp) set to -ENOSYS above */ + cmpq $NR_syscalls, %rax + jae int_ret_from_sys_call /* RAX(%rsp) set to -ENOSYS above */ + sbb %rcx, %rcx /* array_index_mask_nospec() */ + and %rcx, %rax movq %r10,%rcx /* fixup for C */ #ifdef CONFIG_RETPOLINE movq sys_call_table(, %rax, 8), %rax