From: Will Deacon <will@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: Mark Rutland <mark.rutland@arm.com>,
Luis Machado <luis.machado@linaro.org>,
Kees Cook <keescook@chromium.org>, Will Deacon <will@kernel.org>,
catalin.marinas@arm.com, stable@vger.kernel.org,
Keno Fischer <keno@juliacomputing.com>,
kernel-team@android.com
Subject: [PATCH v3 1/7] arm64: ptrace: Consistently use pseudo-singlestep exceptions
Date: Fri, 10 Jul 2020 14:06:56 +0100 [thread overview]
Message-ID: <20200710130702.30658-2-will@kernel.org> (raw)
In-Reply-To: <20200710130702.30658-1-will@kernel.org>
Although the arm64 single-step state machine can be fast-forwarded in
cases where we wish to generate a SIGTRAP without actually executing an
instruction, this has two major limitations outside of simply skipping
an instruction due to emulation.
1. Stepping out of a ptrace signal stop into a signal handler where
SIGTRAP is blocked. Fast-forwarding the stepping state machine in
this case will result in a forced SIGTRAP, with the handler reset to
SIG_DFL.
2. The hardware implicitly fast-forwards the state machine when executing
an SVC instruction for issuing a system call. This can interact badly
with subsequent ptrace stops signalled during the execution of the
system call (e.g. SYSCALL_EXIT or seccomp traps), as they may corrupt
the stepping state by updating the PSTATE for the tracee.
Resolve both of these issues by injecting a pseudo-singlestep exception
on entry to a signal handler and also on return to userspace following a
system call.
Cc: <stable@vger.kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Luis Machado <luis.machado@linaro.org>
Reported-by: Keno Fischer <keno@juliacomputing.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/thread_info.h | 1 +
arch/arm64/kernel/ptrace.c | 25 +++++++++++++++++++------
arch/arm64/kernel/signal.c | 11 ++---------
arch/arm64/kernel/syscall.c | 2 +-
4 files changed, 23 insertions(+), 16 deletions(-)
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 6ea8b6a26ae9..5e784e16ee89 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -93,6 +93,7 @@ void arch_release_task_struct(struct task_struct *tsk);
#define _TIF_SYSCALL_EMU (1 << TIF_SYSCALL_EMU)
#define _TIF_UPROBE (1 << TIF_UPROBE)
#define _TIF_FSCHECK (1 << TIF_FSCHECK)
+#define _TIF_SINGLESTEP (1 << TIF_SINGLESTEP)
#define _TIF_32BIT (1 << TIF_32BIT)
#define _TIF_SVE (1 << TIF_SVE)
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 68b7f34a08f5..057d4aa1af4d 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1818,12 +1818,23 @@ static void tracehook_report_syscall(struct pt_regs *regs,
saved_reg = regs->regs[regno];
regs->regs[regno] = dir;
- if (dir == PTRACE_SYSCALL_EXIT)
+ if (dir == PTRACE_SYSCALL_ENTER) {
+ if (tracehook_report_syscall_entry(regs))
+ forget_syscall(regs);
+ regs->regs[regno] = saved_reg;
+ } else if (!test_thread_flag(TIF_SINGLESTEP)) {
tracehook_report_syscall_exit(regs, 0);
- else if (tracehook_report_syscall_entry(regs))
- forget_syscall(regs);
+ regs->regs[regno] = saved_reg;
+ } else {
+ regs->regs[regno] = saved_reg;
- regs->regs[regno] = saved_reg;
+ /*
+ * Signal a pseudo-step exception since we are stepping but
+ * tracer modifications to the registers may have rewound the
+ * state machine.
+ */
+ tracehook_report_syscall_exit(regs, 1);
+ }
}
int syscall_trace_enter(struct pt_regs *regs)
@@ -1851,12 +1862,14 @@ int syscall_trace_enter(struct pt_regs *regs)
void syscall_trace_exit(struct pt_regs *regs)
{
+ unsigned long flags = READ_ONCE(current_thread_info()->flags);
+
audit_syscall_exit(regs);
- if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
+ if (flags & _TIF_SYSCALL_TRACEPOINT)
trace_sys_exit(regs, regs_return_value(regs));
- if (test_thread_flag(TIF_SYSCALL_TRACE))
+ if (flags & (_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP))
tracehook_report_syscall(regs, PTRACE_SYSCALL_EXIT);
rseq_syscall(regs);
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 801d56cdf701..3b4f31f35e45 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -800,7 +800,6 @@ static void setup_restart_syscall(struct pt_regs *regs)
*/
static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
{
- struct task_struct *tsk = current;
sigset_t *oldset = sigmask_to_save();
int usig = ksig->sig;
int ret;
@@ -824,14 +823,8 @@ static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
*/
ret |= !valid_user_regs(®s->user_regs, current);
- /*
- * Fast forward the stepping logic so we step into the signal
- * handler.
- */
- if (!ret)
- user_fastforward_single_step(tsk);
-
- signal_setup_done(ret, ksig, 0);
+ /* Step into the signal handler if we are stepping */
+ signal_setup_done(ret, ksig, test_thread_flag(TIF_SINGLESTEP));
}
/*
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index 5f5b868292f5..7c14466a12af 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -139,7 +139,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
local_daif_mask();
flags = current_thread_info()->flags;
- if (!has_syscall_work(flags)) {
+ if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP)) {
/*
* We're off to userspace, where interrupts are
* always enabled after we restore the flags from
--
2.27.0.383.g050319c2ae-goog
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next prev parent reply other threads:[~2020-07-10 13:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-10 13:06 [PATCH v3 0/7] arm64: Fix single-step handling and syscall tracing Will Deacon
2020-07-10 13:06 ` Will Deacon [this message]
2020-07-16 0:27 ` [PATCH v3 1/7] arm64: ptrace: Consistently use pseudo-singlestep exceptions Sasha Levin
2020-07-10 13:06 ` [PATCH v3 2/7] arm64: ptrace: Override SPSR.SS when single-stepping is enabled Will Deacon
2020-07-16 0:27 ` Sasha Levin
2020-07-10 13:06 ` [PATCH v3 3/7] arm64: compat: Ensure upper 32 bits of x0 are zero on syscall return Will Deacon
2020-07-16 0:27 ` Sasha Levin
2020-07-10 13:06 ` [PATCH v3 4/7] arm64: ptrace: Add a comment describing our syscall entry/exit trap ABI Will Deacon
2020-07-10 13:07 ` [PATCH v3 5/7] arm64: syscall: Expand the comment about ptrace and syscall(-1) Will Deacon
2020-07-10 13:07 ` [PATCH v3 6/7] arm64: ptrace: Use NO_SYSCALL instead of -1 in syscall_trace_enter() Will Deacon
2020-07-10 16:04 ` Kees Cook
2020-07-10 16:11 ` Will Deacon
2020-07-13 2:32 ` Kees Cook
2020-07-10 13:07 ` [PATCH v3 7/7] arm64: Use test_tsk_thread_flag() for checking TIF_SINGLESTEP Will Deacon
2020-07-14 11:57 ` [PATCH v3 0/7] arm64: Fix single-step handling and syscall tracing Luis Machado
2020-07-15 12:25 ` Luis Machado
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