| 463b7715 | 07-Apr-2023 |
Gregory Price <gourry.memverge@gmail.com> |
syscall_user_dispatch: Untag selector address before access_ok()
To support checkpoint/restart, ptrace must be able to set the selector
of the tracee. The selector is a user pointer that may be sub
syscall_user_dispatch: Untag selector address before access_ok()
To support checkpoint/restart, ptrace must be able to set the selector
of the tracee. The selector is a user pointer that may be subject to
memory tagging extensions on some architectures (namely ARM MTE).
access_ok() clears memory tags for tagged addresses if the current task has
memory tagging enabled.
This obviously fails when ptrace modifies the selector of a tracee when
tracer and tracee do not have the same memory tagging enabled state.
Solve this by untagging the selector address before handing it to
access_ok(), like other ptrace functions which modify tracee pointers do.
Obviously a tracer can set an invalid selector address for the tracee, but
that's independent of tagging and a general capability of the tracer.
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Gregory Price <gregory.price@memverge.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/all/ZCWXE04nLZ4pXEtM@arm.com/
Link: https://lore.kernel.org/r/20230407171834.3558-3-gregory.price@memverge.com
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| b4165140 | 15-Mar-2023 |
Frederic Weisbecker <frederic@kernel.org> |
entry/rcu: Check TIF_RESCHED _after_ delayed RCU wake-up
RCU sometimes needs to perform a delayed wake up for specific kthreads
handling offloaded callbacks (RCU_NOCB). These wakeups are performed
entry/rcu: Check TIF_RESCHED _after_ delayed RCU wake-up
RCU sometimes needs to perform a delayed wake up for specific kthreads
handling offloaded callbacks (RCU_NOCB). These wakeups are performed
by timers and upon entry to idle (also to guest and to user on nohz_full).
However the delayed wake-up on kernel exit is actually performed after
the thread flags are fetched towards the fast path check for work to
do on exit to user. As a result, and if there is no other pending work
to do upon that kernel exit, the current task will resume to userspace
with TIF_RESCHED set and the pending wake up ignored.
Fix this with fetching the thread flags _after_ the delayed RCU-nocb
kthread wake-up.
Fixes: 47b8ff194c1f ("entry: Explicitly flush pending rcuog wakeup before last rescheduling point")
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230315194349.10798-3-joel@joelfernandes.org
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| 0cfcb2b9 | 27-Jan-2022 |
Eric W. Biederman <ebiederm@xmission.com> |
ptrace: Remove arch_syscall_{enter,exit}_tracehook
These functions are alwasy one-to-one wrappers around
ptrace_report_syscall_entry and ptrace_report_syscall_exit.
So directly call the functions th
ptrace: Remove arch_syscall_{enter,exit}_tracehook
These functions are alwasy one-to-one wrappers around
ptrace_report_syscall_entry and ptrace_report_syscall_exit.
So directly call the functions they are wrapping instead.
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20220309162454.123006-4-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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| 99cf983c | 14-Feb-2022 |
Mark Rutland <mark.rutland@arm.com> |
sched/preempt: Add PREEMPT_DYNAMIC using static keys
Where an architecture selects HAVE_STATIC_CALL but not
HAVE_STATIC_CALL_INLINE, each static call has an out-of-line trampoline
which will either
sched/preempt: Add PREEMPT_DYNAMIC using static keys
Where an architecture selects HAVE_STATIC_CALL but not
HAVE_STATIC_CALL_INLINE, each static call has an out-of-line trampoline
which will either branch to a callee or return to the caller.
On such architectures, a number of constraints can conspire to make
those trampolines more complicated and potentially less useful than we'd
like. For example:
* Hardware and software control flow integrity schemes can require the
addition of "landing pad" instructions (e.g. `BTI` for arm64), which
will also be present at the "real" callee.
* Limited branch ranges can require that trampolines generate or load an
address into a register and perform an indirect branch (or at least
have a slow path that does so). This loses some of the benefits of
having a direct branch.
* Interaction with SW CFI schemes can be complicated and fragile, e.g.
requiring that we can recognise idiomatic codegen and remove
indirections understand, at least until clang proves more helpful
mechanisms for dealing with this.
For PREEMPT_DYNAMIC, we don't need the full power of static calls, as we
really only need to enable/disable specific preemption functions. We can
achieve the same effect without a number of the pain points above by
using static keys to fold early returns into the preemption functions
themselves rather than in an out-of-line trampoline, effectively
inlining the trampoline into the start of the function.
For arm64, this results in good code generation. For example, the
dynamic_cond_resched() wrapper looks as follows when enabled. When
disabled, the first `B` is replaced with a `NOP`, resulting in an early
return.
| <dynamic_cond_resched>:
| bti c
| b <dynamic_cond_resched+0x10> // or `nop`
| mov w0, #0x0
| ret
| mrs x0, sp_el0
| ldr x0, [x0, #8]
| cbnz x0, <dynamic_cond_resched+0x8>
| paciasp
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl <preempt_schedule_common>
| mov w0, #0x1
| ldp x29, x30, [sp], #16
| autiasp
| ret
... compared to the regular form of the function:
| <__cond_resched>:
| bti c
| mrs x0, sp_el0
| ldr x1, [x0, #8]
| cbz x1, <__cond_resched+0x18>
| mov w0, #0x0
| ret
| paciasp
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl <preempt_schedule_common>
| mov w0, #0x1
| ldp x29, x30, [sp], #16
| autiasp
| ret
Any architecture which implements static keys should be able to use this
to implement PREEMPT_DYNAMIC with similar cost to non-inlined static
calls. Since this is likely to have greater overhead than (inlined)
static calls, PREEMPT_DYNAMIC is only defaulted to enabled when
HAVE_PREEMPT_DYNAMIC_CALL is selected.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20220214165216.2231574-6-mark.rutland@arm.com
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