Currently we treat the alternatives separately from other data that's
only used during initialisation, using separate .altinstructions and
.altinstr_replacement linker sections. These are freed for general
allocation separately from .init*. This is problematic as:
* We do not remove execute permissions, as we do for .init, leaving the
memory executable.
* We pad between them, making the kernel Image bianry up to PAGE_SIZE
bytes larger than necessary.
This patch moves the two sections into the contiguous region used for
.init*. This saves some memory, ensures that we remove execute
permissions, and allows us to remove some code made redundant by this
reorganisation.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jeremy Linton <jeremy.linton@arm.com>
Cc: Laura Abbott <labbott@fedoraproject.org>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
In order to guarantee that the patched instruction stream is visible to
a CPU, that CPU must execute an isb instruction after any related cache
maintenance has completed.
The instruction patching routines in kernel/insn.c get this right for
things like jump labels and ftrace, but the alternatives patching omits
it entirely leaving secondary cores in a potential limbo between the old
and the new code.
This patch adds an isb following the secondary polling loop in the
altenatives patching.
Signed-off-by: Will Deacon <will.deacon@arm.com>
When patching the kernel text with alternatives, we may end up patching
parts of the stop_machine state machine (e.g. atomic_dec_and_test in
ack_state) and consequently corrupt the instruction stream of any
secondary CPUs.
This patch passes the cpu_online_mask to stop_machine, forcing all of
the CPUs into our own callback which can place the secondary cores into
a dumb (but safe!) polling loop whilst the patching is carried out.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Since all branches are PC-relative on AArch64, these instructions
cannot be used as an alternative with the simplistic approach
we currently have (the immediate has been computed from
the .altinstr_replacement section, and end-up being completely off
if the target is outside of the replacement sequence).
This patch handles the branch instructions in a different way,
using the insn framework to recompute the immediate, and generate
the right displacement in the above case.
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This reverts most of commit fef7f2b201.
It turns out that there are a couple of problems with the way we're
fixing up branch instructions used as part of alternative instruction
sequences:
(1) If the branch target is also in the alternative sequence, we'll
generate a branch into the .altinstructions section which actually
gets freed.
(2) The calls to aarch64_insn_{read,write} bring an awful lot more
code into the patching path (e.g. taking locks, poking the fixmap,
invalidating the TLB) which isn't actually needed for the early
patching run under stop_machine, but makes the use of alternative
sequences extremely fragile (as we can't patch code that could be
used by the patching code).
Given that no code actually requires alternative patching of immediate
branches, let's remove this support for now and revisit it when we've
got a user. We leave the updated size check, since we really do require
the sequences to be the same length.
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Since all immediate branches are PC-relative on Aarch64, these
instructions cannot be used as an alternative with the simplistic
approach we currently have (the immediate has been computed from
the .altinstr_replacement section, and end-up being completely off
if we insert it directly).
This patch handles the b and bl instructions in a different way,
using the insn framework to recompute the immediate, and generate
the right displacement.
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Currently the kernel patches all necessary instructions once at boot
time, so modules are not covered by this.
Change the apply_alternatives() function to take a beginning and an
end pointer and introduce a new variant (apply_alternatives_all()) to
cover the existing use case for the static kernel image section.
Add a module_finalize() function to arm64 to check for an
alternatives section in a module and patch only the instructions from
that specific area.
Since that module code is not touched before the module
initialization has ended, we don't need to halt the machine before
doing the patching in the module's code.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
With a blatant copy of some x86 bits we introduce the alternative
runtime patching "framework" to arm64.
This is quite basic for now and we only provide the functions we need
at this time.
This is connected to the newly introduced feature bits.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
