There are two outstanding issues with CONFIG_X86_X32_ABI and
llvm-objcopy, with similar root causes:
1. llvm-objcopy does not properly convert .note.gnu.property when going
from x86_64 to x86_x32, resulting in a corrupted section when
linking:
https://github.com/ClangBuiltLinux/linux/issues/1141
2. llvm-objcopy produces corrupted compressed debug sections when going
from x86_64 to x86_x32, also resulting in an error when linking:
https://github.com/ClangBuiltLinux/linux/issues/514
After commit 41c5ef31ad71 ("x86/ibt: Base IBT bits"), the
.note.gnu.property section is always generated when
CONFIG_X86_KERNEL_IBT is enabled, which causes the first issue to become
visible with an allmodconfig build:
ld.lld: error: arch/x86/entry/vdso/vclock_gettime-x32.o:(.note.gnu.property+0x1c): program property is too short
To avoid this error, do not allow CONFIG_X86_X32_ABI to be selected when
using llvm-objcopy. If the two issues ever get fixed in llvm-objcopy,
this can be turned into a feature check.
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220314194842.3452-3-nathan@kernel.org
Commit 0bf6276392 ("x32: Warn and disable rather than error if
binutils too old") added a small test in arch/x86/Makefile because
binutils 2.22 or newer is needed to properly support elf32-x86-64. This
check is no longer necessary, as the minimum supported version of
binutils is 2.23, which is enforced at configuration time with
scripts/min-tool-version.sh.
Remove this check and replace all uses of CONFIG_X86_X32 with
CONFIG_X86_X32_ABI, as two symbols are no longer necessary.
[nathan: Rebase, fix up a few places where CONFIG_X86_X32 was still
used, and simplify commit message to satisfy -tip requirements]
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220314194842.3452-2-nathan@kernel.org
Objtool's --ibt option generates .ibt_endbr_seal which lists
superfluous ENDBR instructions. That is those instructions for which
the function is never indirectly called.
Overwrite these ENDBR instructions with a NOP4 such that these
function can never be indirect called, reducing the number of viable
ENDBR targets in the kernel.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154319.822545231@infradead.org
Intel IBT requires that every indirect JMP/CALL targets an ENDBR
instructions, failing this #CP happens and we die. Similarly, all
exception entries should be ENDBR.
Find all code relocations and ensure they're either an ENDBR
instruction or ANNOTATE_NOENDBR. For the exceptions look for
UNWIND_HINT_IRET_REGS at sym+0 not being ENDBR.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154319.705110141@infradead.org
Intel IBT requires the target of any indirect CALL or JMP instruction
to be the ENDBR instruction; optionally it allows those two
instructions to have a NOTRACK prefix in order to avoid this
requirement.
The kernel will not enable the use of NOTRACK, as such any occurence
of it in compiler generated code should be flagged.
Teach objtool to Decode ENDBR instructions and WARN about NOTRACK
prefixes.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154319.645963517@infradead.org
Currently ASM_REACHABLE only works for UD2 instructions; reorder
things to also allow over-riding dead_end_function().
To that end:
- Mark INSN_BUG instructions in decode_instructions(), this saves
having to iterate all instructions yet again.
- Have add_call_destinations() set insn->dead_end for
dead_end_function() calls.
- Move add_dead_ends() *after* add_call_destinations() such that
ASM_REACHABLE can clear the ->dead_end mark.
- have validate_branch() only check ->dead_end.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154319.410010807@infradead.org
There's a fun implementation detail on linking STB_WEAK symbols. When
the linker combines two translation units, where one contains a weak
function and the other an override for it. It simply strips the
STB_WEAK symbol from the symbol table, but doesn't actually remove the
code.
The result is that when objtool is ran in a whole-archive kind of way,
it will encounter *heaps* of unused (and unreferenced) code. All
rudiments of weak functions.
Additionally, when a weak implementation is split into a .cold
subfunction that .cold symbol is left in place, even though completely
unused.
Teach objtool to ignore such rudiments by searching for symbol holes;
that is, code ranges that fall outside the given symbol bounds.
Specifically, ignore a sequence of unreachable instruction iff they
occupy a single hole, additionally ignore any .cold subfunctions
referenced.
Both ld.bfd and ld.lld behave like this. LTO builds otoh can (and do)
properly DCE weak functions.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154319.232019347@infradead.org
With IBT enabled builds we need ENDBR instructions at indirect jump
target sites, since we start execution of the JIT'ed code through an
indirect jump, the very first instruction needs to be ENDBR.
Similarly, since eBPF tail-calls use indirect branches, their landing
site needs to be an ENDBR too.
The trampolines need similar adjustment.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Fixed-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.464998838@infradead.org
In order to allow kprobes to skip the ENDBR instructions at sym+0 for
X86_KERNEL_IBT builds, change _kprobe_addr() to take an architecture
callback to inspect the function at hand and modify the offset if
needed.
This streamlines the existing interface to cover more cases and
require less hooks. Once PowerPC gets fully converted there will only
be the one arch hook.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.405947704@infradead.org
Return trampoline must not use indirect branch to return; while this
preserves the RSB, it is fundamentally incompatible with IBT. Instead
use a retpoline like ROP gadget that defeats IBT while not unbalancing
the RSB.
And since ftrace_stub is no longer a plain RET, don't use it to copy
from. Since RET is a trivial instruction, poke it directly.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.347296408@infradead.org
Currently a lot of ftrace code assumes __fentry__ is at sym+0. However
with Intel IBT enabled the first instruction of a function will most
likely be ENDBR.
Change ftrace_location() to not only return the __fentry__ location
when called for the __fentry__ location, but also when called for the
sym+0 location.
Then audit/update all callsites of this function to consistently use
these new semantics.
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.227581603@infradead.org
Kernel entry points should be having ENDBR on for IBT configs.
The SYSCALL entry points are found through taking their respective
address in order to program them in the MSRs, while the exception
entry points are found through UNWIND_HINT_IRET_REGS.
The rule is that any UNWIND_HINT_IRET_REGS at sym+0 should have an
ENDBR, see the later objtool ibt validation patch.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154317.933157479@infradead.org
Even though Xen currently doesn't advertise IBT, prepare for when it
will eventually do so and sprinkle the ENDBR dust accordingly.
Even though most of the entry points are IRET like, the CPL0
Hypervisor can set WAIT-FOR-ENDBR and demand ENDBR at these sites.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154317.873919996@infradead.org
Add Kconfig, Makefile and basic instruction support for x86 IBT.
(Ab)use __DISABLE_EXPORTS to disable IBT since it's already employed
to mark compressed and purgatory. Additionally mark realmode with it
as well to avoid inserting ENDBR instructions there. While ENDBR is
technically a NOP, inserting them was causing some grief due to code
growth. There's also a problem with using __noendbr in code compiled
without -fcf-protection=branch.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154317.519875203@infradead.org
The current annotation relies on not running objtool on the file; this
won't work when running objtool on vmlinux.o. Instead explicitly mark
__efi64_thunk() to be ignored.
This preserves the status quo, which is somewhat unfortunate. Luckily
this code is hardly ever used.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154317.402118218@infradead.org
The ENQCMD instruction implicitly accesses the PASID_MSR to fill in the
pasid field of the descriptor being submitted to an accelerator. But
there is no precise (and stable across kernel changes) point at which
the PASID_MSR is updated from the value for one task to the next.
Kernel code that uses accelerators must always use the ENQCMDS instruction
which does not access the PASID_MSR.
Check for use of the ENQCMD instruction in the kernel and warn on its
usage.
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220207230254.3342514-11-fenghua.yu@intel.com
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
