> -----Original Message----- > From: Jiri Kosina [mailto:ji...@kernel.org] > Sent: Wednesday, September 12, 2018 2:05 AM > To: Thomas Gleixner <t...@linutronix.de>; Ingo Molnar <mi...@redhat.com>; > Peter Zijlstra <pet...@infradead.org>; Josh Poimboeuf > <jpoim...@redhat.com>; Andrea Arcangeli <aarca...@redhat.com>; > Woodhouse, David <d...@amazon.co.uk>; Andi Kleen <a...@linux.intel.com>; > Tim Chen <tim.c.c...@linux.intel.com>; Schaufler, Casey > <casey.schauf...@intel.com> > Cc: linux-kernel@vger.kernel.org; x...@kernel.org > Subject: [PATCH v6 0/3] Harden spectrev2 userspace-userspace protection > > Currently, linux kernel is basically not preventing userspace-userspace > spectrev2 attack, because: > > - IBPB is basically unused (issued only for tasks that marked themselves > explicitly non-dumpable, which is absolutely negligible minority of all > software out there), therefore cross-process branch buffer posioning > using spectrev2 is possible > > - STIBP is completely unused, therefore cross-process branch buffer > poisoning using spectrev2 between processess running on two HT siblings > thread s is possible > > This patchset changes IBPB semantics, so that it's now applied whenever > context-switching between processess that can't use ptrace() to achieve > the same. This admittedly comes with extra overhad on a context switch; > systems that don't care about could disable the mitigation using > nospectre_v2 boot option. > The IBPB implementaion is heavily based on original patches by Tim Chen. > > In addition to that, we unconditionally turn STIBP on so that HT siblings > always have separate branch buffers. > > We've been carrying IBPB implementation with the same semantics in our > (SUSE) trees since january disclosure; STIBP was more or less ignored up > to today. > > v1->v2: > include IBPB changes > v2->v3: > fix IBPB 'who can trace who' semantics > wire up STIBP flipping to SMT hotplug > v3->v4: > dropped ___ptrace_may_access(), as it's not needed > fixed deadlock with LSM/audit/selinux (Andrea Arcangeli) > statically patch out the ptrace check if !IBPB > > v4->v5: > fix MSR writing logic (Thomas Gleixner, Josh Poimboeuf) > > v5->v6: > propagate X86_FEATURE_RSB_CTXSW setting to sysfs > propagate STIBP setting to sysfs (Thomas Gleixner) > simplify arch_smt_update() (Thomas Gleixner) > > Jiri Kosina (3): > x86/speculation: apply IBPB more strictly to avoid cross-process data > leak > x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation > x86/speculation: Propagate information about RSB filling mitigation to > sysfs > > arch/x86/kernel/cpu/bugs.c | 60 > ++++++++++++++++++++++++++++++++++++++++++++++++++++++------ > arch/x86/mm/tlb.c | 31 ++++++++++++++++++++----------- > include/linux/ptrace.h | 4 ++++ > kernel/cpu.c | 11 ++++++++++- > kernel/ptrace.c | 12 ++++++++---- > 5 files changed, 96 insertions(+), 22 deletions(-) > > -- > Jiri Kosina > SUSE Labs
The locking issue with SELinux has a simple fix as below.
The other LSMs don't manifest this issue. With the change to
SELinux the call to security_ptrace_access_check() can and
should be made unconditionally.
Patch is attached, whitespace damaged (known problem) patch:
SELinux: Handle audit locking for PTRACE_MODE_IBPB
The SELinux audit code locking cannot be used from the
task switching code, which is where PTRACE_MODE_IBPB comes
from. As this is a system check, not a user action, audit
is not needed, and would generate noise. Use the unaudited
check for this case.
Signed-off-by: Casey Schaufler <casey.schauf...@intel.com>
---
kernel/ptrace.c | 4 +---
security/selinux/hooks.c | 5 +++++
2 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 5c5e7cb597cd..202a4d9c2af7 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -330,9 +330,7 @@ int __ptrace_may_access(struct task_struct *task, unsigned
int mode)
!ptrace_has_cap(mm->user_ns, mode))))
return -EPERM;
- if (!(mode & PTRACE_MODE_NOACCESS_CHK))
- return security_ptrace_access_check(task, mode);
- return 0;
+ return security_ptrace_access_check(task, mode);
}
bool ptrace_may_access(struct task_struct *task, unsigned int mode)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 161a4f29f860..30d21142e9fe 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2215,7 +2215,12 @@ static int selinux_ptrace_access_check(struct
task_struct *child,
{
u32 sid = current_sid();
u32 csid = task_sid(child);
+ struct av_decision avd;
+ if (mode == PTRACE_MODE_IBPB)
+ return avc_has_perm_noaudit(&selinux_state, sid, csid,
+ SECCLASS_PROCESS, PROCESS__PTRACE,
+ 0, &avd);
if (mode & PTRACE_MODE_READ)
return avc_has_perm(&selinux_state,
sid, csid, SECCLASS_FILE, FILE__READ, NULL);
casey-jiri-v6.patch
Description: casey-jiri-v6.patch
