linux-toradex.git/kernel/rseq.c, branch v5.19-rc1

rseq: Remove broken uapi field layout on 32-bit little endian

2022-02-02T12:11:34+00:00

The rseq rseq_cs.ptr.{ptr32,padding} uapi endianness handling is
entirely wrong on 32-bit little endian: a preprocessor logic mistake
wrongly uses the big endian field layout on 32-bit little endian
architectures.

Fortunately, those ptr32 accessors were never used within the kernel,
and only meant as a convenience for user-space.

Remove those and replace the whole rseq_cs union by a __u64 type, as
this is the only thing really needed to express the ABI. Document how
32-bit architectures are meant to interact with this field.

Fixes: ec9c82e03a74 ("rseq: uapi: Declare rseq_cs field as union, update includes")
Signed-off-by: Mathieu Desnoyers 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20220127152720.25898-1-mathieu.desnoyers@efficios.com

KVM: rseq: Update rseq when processing NOTIFY_RESUME on xfer to KVM guest

2021-09-22T14:24:01+00:00

Invoke rseq's NOTIFY_RESUME handler when processing the flag prior to
transferring to a KVM guest, which is roughly equivalent to an exit to
userspace and processes many of the same pending actions.  While the task
cannot be in an rseq critical section as the KVM path is reachable only
by via ioctl(KVM_RUN), the side effects that apply to rseq outside of a
critical section still apply, e.g. the current CPU needs to be updated if
the task is migrated.

Clearing TIF_NOTIFY_RESUME without informing rseq can lead to segfaults
and other badness in userspace VMMs that use rseq in combination with KVM,
e.g. due to the CPU ID being stale after task migration.

Fixes: 72c3c0fe54a3 ("x86/kvm: Use generic xfer to guest work function")
Reported-by: Peter Foley 
Bisected-by: Doug Evans 
Acked-by: Mathieu Desnoyers 
Cc: Shakeel Butt 
Cc: Thomas Gleixner 
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson 
Message-Id: <20210901203030.1292304-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini

rseq: Optimise rseq_get_rseq_cs() and clear_rseq_cs()

2021-04-14T16:04:09+00:00

Commit ec9c82e03a74 ("rseq: uapi: Declare rseq_cs field as union,
update includes") added regressions for our servers.

Using copy_from_user() and clear_user() for 64bit values
is suboptimal.

We can use faster put_user() and get_user() on 64bit arches.

Signed-off-by: Eric Dumazet 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Mathieu Desnoyers 
Link: https://lkml.kernel.org/r/20210413203352.71350-4-eric.dumazet@gmail.com

rseq: Remove redundant access_ok()

2021-04-14T16:04:09+00:00

After commit 8f2817701492 ("rseq: Use get_user/put_user rather
than __get_user/__put_user") we no longer need
an access_ok() call from __rseq_handle_notify_resume()

Mathieu pointed out the same cleanup can be done
in rseq_syscall().

Signed-off-by: Eric Dumazet 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Mathieu Desnoyers 
Link: https://lkml.kernel.org/r/20210413203352.71350-3-eric.dumazet@gmail.com

rseq: Optimize rseq_update_cpu_id()

2021-04-14T16:04:09+00:00

Two put_user() in rseq_update_cpu_id() are replaced
by a pair of unsafe_put_user() with appropriate surroundings.

This removes one stac/clac pair on x86 in fast path.

Signed-off-by: Eric Dumazet 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Mathieu Desnoyers 
Link: https://lkml.kernel.org/r/20210413203352.71350-2-eric.dumazet@gmail.com

rseq: Reject unknown flags on rseq unregister

2019-12-25T09:41:20+00:00

It is preferrable to reject unknown flags within rseq unregistration
rather than to ignore them. It is an oversight caused by the fact that
the check for unknown flags is after the rseq unregister flag check.

Signed-off-by: Mathieu Desnoyers 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20191211161713.4490-2-mathieu.desnoyers@efficios.com
Signed-off-by: Ingo Molnar

signal: Remove task parameter from force_sig

2019-05-27T14:36:28+00:00

All of the remaining callers pass current into force_sig so
remove the task parameter to make this obvious and to make
misuse more difficult in the future.

This also makes it clear force_sig passes current into force_sig_info.

Signed-off-by: "Eric W. Biederman"

signal: Remove task parameter from force_sigsegv

2019-05-27T14:36:28+00:00

The function force_sigsegv is always called on the current task
so passing in current is redundant and not passing in current
makes this fact obvious.

This also makes it clear force_sigsegv always calls force_sig
on the current task.

Signed-off-by: "Eric W. Biederman"

rseq: Remove superfluous rseq_len from task_struct

2019-04-19T10:39:32+00:00

The rseq system call, when invoked with flags of "0" or
"RSEQ_FLAG_UNREGISTER" values, expects the rseq_len parameter to
be equal to sizeof(struct rseq), which is fixed-size and fixed-layout,
specified in uapi linux/rseq.h.

Expecting a fixed size for rseq_len is a design choice that ensures
multiple libraries and application defining __rseq_abi in the same
process agree on its exact size.

Considering that this size is and will always be the same value, there
is no point in saving this value within task_struct rseq_len. Remove
this field from task_struct.

No change in functionality intended.

Signed-off-by: Mathieu Desnoyers 
Acked-by: Peter Zijlstra (Intel) 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Ben Maurer 
Cc: Boqun Feng 
Cc: Catalin Marinas 
Cc: Chris Lameter 
Cc: Dave Watson 
Cc: H. Peter Anvin 
Cc: Joel Fernandes 
Cc: Josh Triplett 
Cc: Linus Torvalds 
Cc: Michael Kerrisk 
Cc: Paul E. McKenney 
Cc: Paul Turner 
Cc: Peter Zijlstra 
Cc: Russell King 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Will Deacon 
Cc: linux-api@vger.kernel.org
Link: http://lkml.kernel.org/r/20190305194755.2602-3-mathieu.desnoyers@efficios.com
Signed-off-by: Ingo Molnar

rseq: Clean up comments by reflecting removal of event counter

2019-04-19T10:39:31+00:00

The "event counter" was removed from rseq before it was merged upstream.
However, a few comments in the source code still refer to it. Adapt the
comments to match reality.

Signed-off-by: Mathieu Desnoyers 
Acked-by: Peter Zijlstra (Intel) 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Ben Maurer 
Cc: Boqun Feng 
Cc: Catalin Marinas 
Cc: Chris Lameter 
Cc: Dave Watson 
Cc: H. Peter Anvin 
Cc: Joel Fernandes 
Cc: Josh Triplett 
Cc: Linus Torvalds 
Cc: Michael Kerrisk 
Cc: Paul E. McKenney 
Cc: Paul Turner 
Cc: Peter Zijlstra 
Cc: Russell King 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Will Deacon 
Cc: linux-api@vger.kernel.org
Link: http://lkml.kernel.org/r/20190305194755.2602-2-mathieu.desnoyers@efficios.com
Signed-off-by: Ingo Molnar