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  1. 09 Jul, 2020 2 commits
  3. 08 Jul, 2020 11 commits
  5. 03 Jul, 2020 3 commits
  7. 02 Jul, 2020 1 commit
    • Ard Biesheuvel's avatar
      arm64/alternatives: use subsections for replacement sequences · f7b93d42
      Ard Biesheuvel authored 
      When building very large kernels, the logic that emits replacement
sequences for alternatives fails when relative branches are present
in the code that is emitted into the .altinstr_replacement section
and patched in at the original site and fixed up. The reason is that
the linker will insert veneers if relative branches go out of range,
and due to the relative distance of the .altinstr_replacement from
the .text section where its branch targets usually live, veneers
may be emitted at the end of the .altinstr_replacement section, with
the relative branches in the sequence pointed at the veneers instead
of the actual target.

The alternatives patching logic will attempt to fix up the branch to
point to its original target, which will be the veneer in this case,
but given that the patch site is likely to be far away as well, it
will be out of range and so patching will fail. There are other cases
where these veneers are problematic, e.g., when the target of the
branch is in .text while the patch site is in .init.text, in which
case putting the replacement sequence inside .text may not help either.

So let's use subsections to emit the replacement code as closely as
possible to the patch site, to ensure that veneers are only likely to
be emitted if they are required at the patch site as well, in which
case they will be in range for the replacement sequence both before
and after it is transported to the patch site.

This will prevent alternative sequences in non-init code from being
released from memory after boot, but this is tolerable given that the
entire section is only 512 KB on an allyesconfig build (which weighs in
at 500+ MB for the entire Image). Also, note that modules today carry
the replacement sequences in non-init sections as well, and any of
those that target init code will be emitted into init sections after
this change.

This fixes an early crash when booting an allyesconfig kernel on a
system where any of the alternatives sequences containing relative
branches are activated at boot (e.g., ARM64_HAS_PAN on TX2)
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Dave P Martin <dave.martin@arm.com>
Link: https://lore.kernel.org/r/20200630081921.13443-1-ardb@kernel.orgSigned-off-by: default avatarWill Deacon <will@kernel.org>
      f7b93d42
  9. 25 Jun, 2020 2 commits
  11. 24 Jun, 2020 5 commits
  13. 23 Jun, 2020 5 commits
    • Mark Brown's avatar
      arm64: Depend on newer binutils when building PAC · 4dc9b282
      Mark Brown authored 
      Versions of binutils prior to 2.33.1 don't understand the ELF notes that
are added by modern compilers to indicate the PAC and BTI options used
to build the code. This causes them to emit large numbers of warnings in
the form:

aarch64-linux-gnu-nm: warning: .tmp_vmlinux.kallsyms2: unsupported GNU_PROPERTY_TYPE (5) type: 0xc0000000

during the kernel build which is currently causing quite a bit of
disruption for automated build testing using clang.

In commit 15cd0e67 (arm64: Kconfig: ptrauth: Add binutils version
check to fix mismatch) we added a dependency on binutils to avoid this
issue when building with versions of GCC that emit the notes but did not
do so for clang as it was believed that the existing check for
.cfi_negate_ra_state was already requiring a new enough binutils. This
does not appear to be the case for some versions of binutils (eg, the
binutils in Debian 10) so instead refactor so we require a new enough
GNU binutils in all cases other than when we are using an old GCC
version that does not emit notes.

Other, more exotic, combinations of tools are possible such as using
clang, lld and gas together are possible and may have further problems
but rather than adding further version checks it looks like the most
robust thing will be to just test that we can build cleanly with the
configured tools but that will require more review and discussion so do
this for now to address the immediate problem disrupting build testing.
Reported-by: default avatarKernelCI <bot@kernelci.org>
Reported-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Signed-off-by: default avatarMark Brown <broonie@kernel.org>
Reviewed-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/1054
Link: https://lore.kernel.org/r/20200619123550.48098-1-broonie@kernel.orgSigned-off-by: default avatarWill Deacon <will@kernel.org>
      4dc9b282
    • Will Deacon's avatar
      arm64: compat: Remove 32-bit sigreturn code from the vDSO · 2d071968
      Will Deacon authored 
      The sigreturn code in the compat vDSO is unused. Remove it.
Reviewed-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: default avatarArd Biesheuvel <ardb@kernel.org>
Reviewed-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
      2d071968
    • Will Deacon's avatar
      arm64: compat: Always use sigpage for sigreturn trampoline · 8e411be6
      Will Deacon authored 
      The 32-bit sigreturn trampoline in the compat sigpage matches the binary
representation of the arch/arm/ sigpage exactly. This is important for
debuggers (e.g. GDB) and unwinders (e.g. libunwind) since they rely
on matching the instruction sequence in order to identify that they are
unwinding through a signal. The same cannot be said for the sigreturn
trampoline in the compat vDSO, which defeats the unwinder heuristics and
instead attempts to use unwind directives for the unwinding. This is in
contrast to arch/arm/, which never uses the vDSO for sigreturn.

Ensure compatibility with arch/arm/ and existing unwinders by always
using the sigpage for the sigreturn trampoline, regardless of the
presence of the compat vDSO.
Reviewed-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: default avatarArd Biesheuvel <ardb@kernel.org>
Reviewed-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
      8e411be6
    • Will Deacon's avatar
      arm64: compat: Allow 32-bit vdso and sigpage to co-exist · a39060b0
      Will Deacon authored 
      In preparation for removing the signal trampoline from the compat vDSO,
allow the sigpage and the compat vDSO to co-exist.

For the moment the vDSO signal trampoline will still be used when built.
Subsequent patches will move to the sigpage consistently.
Acked-by: default avatarDave Martin <Dave.Martin@arm.com>
Reviewed-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: default avatarArd Biesheuvel <ardb@kernel.org>
Reviewed-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
      a39060b0
    • Will Deacon's avatar
      arm64: vdso: Disable dwarf unwinding through the sigreturn trampoline · 87676cfc
      Will Deacon authored 
      Commit 7e9f5e66 ("arm64: vdso: Add --eh-frame-hdr to ldflags") results
in a .eh_frame_hdr section for the vDSO, which in turn causes the libgcc
unwinder to unwind out of signal handlers using the .eh_frame information
populated by our .cfi directives. In conjunction with a4eb355a
("arm64: vdso: Fix CFI directives in sigreturn trampoline"), this has
been shown to cause segmentation faults originating from within the
unwinder during thread cancellation:

 | Thread 14 "virtio-net-rx" received signal SIGSEGV, Segmentation fault.
 | 0x0000000000435e24 in uw_frame_state_for ()
 | (gdb) bt
 | #0  0x0000000000435e24 in uw_frame_state_for ()
 | #1  0x0000000000436e88 in _Unwind_ForcedUnwind_Phase2 ()
 | #2  0x00000000004374d8 in _Unwind_ForcedUnwind ()
 | #3  0x0000000000428400 in __pthread_unwind (buf=<optimized out>) at unwind.c:121
 | #4  0x0000000000429808 in __do_cancel () at ./pthreadP.h:304
 | #5  sigcancel_handler (sig=32, si=0xffff33c743f0, ctx=<optimized out>) at nptl-init.c:200
 | #6  sigcancel_handler (sig=<optimized out>, si=0xffff33c743f0, ctx=<optimized out>) at nptl-init.c:165
 | #7  <signal handler called>
 | #8  futex_wait_cancelable (private=0, expected=0, futex_word=0x3890b708) at ../sysdeps/unix/sysv/linux/futex-internal.h:88

After considerable bashing of heads, it appears that our CFI directives
for unwinding out of the sigreturn trampoline are only processed by libgcc
when both a .eh_frame_hdr section is present *and* the mysterious NOP is
covered by an entry in .eh_frame. With both of these now in place, it has
highlighted that our CFI directives are not comprehensive enough to
restore the stack pointer of the interrupted context. This results in libgcc
falling back to an arm64-specific unwinder after computing a bogus PC value
from the unwind tables. The unwinder promptly dereferences this bogus address
in an attempt to see if the pointed-to instruction sequence looks like
the sigreturn trampoline.

Restore the old unwind behaviour, which relied solely on heuristics in
the unwinder, by removing the .eh_frame_hdr section from the vDSO and
commenting out the insufficient CFI directives for now. Add comments to
explain the current, miserable state of affairs.

Cc: Tamas Zsoldos <tamas.zsoldos@arm.com>
Cc: Szabolcs Nagy <szabolcs.nagy@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Daniel Kiss <daniel.kiss@arm.com>
Acked-by: default avatarDave Martin <Dave.Martin@arm.com>
Reviewed-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: default avatarArd Biesheuvel <ardb@kernel.org>
Reported-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
      87676cfc
  15. 18 Jun, 2020 3 commits
  17. 17 Jun, 2020 1 commit
    • Will Deacon's avatar
      arm64: bti: Require clang >= 10.0.1 for in-kernel BTI support · b9249cba
      Will Deacon authored 
      Unfortunately, most versions of clang that support BTI are capable of
miscompiling the kernel when converting a switch statement into a jump
table. As an example, attempting to spawn a KVM guest results in a panic:

[   56.253312] Kernel panic - not syncing: bad mode
[   56.253834] CPU: 0 PID: 279 Comm: lkvm Not tainted 5.8.0-rc1 #2
[   56.254225] Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
[   56.254712] Call trace:
[   56.254952]  dump_backtrace+0x0/0x1d4
[   56.255305]  show_stack+0x1c/0x28
[   56.255647]  dump_stack+0xc4/0x128
[   56.255905]  panic+0x16c/0x35c
[   56.256146]  bad_el0_sync+0x0/0x58
[   56.256403]  el1_sync_handler+0xb4/0xe0
[   56.256674]  el1_sync+0x7c/0x100
[   56.256928]  kvm_vm_ioctl_check_extension_generic+0x74/0x98
[   56.257286]  __arm64_sys_ioctl+0x94/0xcc
[   56.257569]  el0_svc_common+0x9c/0x150
[   56.257836]  do_el0_svc+0x84/0x90
[   56.258083]  el0_sync_handler+0xf8/0x298
[   56.258361]  el0_sync+0x158/0x180

This is because the switch in kvm_vm_ioctl_check_extension_generic()
is executed as an indirect branch to tail-call through a jump table:

ffff800010032dc8:       3869694c        ldrb    w12, [x10, x9]
ffff800010032dcc:       8b0c096b        add     x11, x11, x12, lsl #2
ffff800010032dd0:       d61f0160        br      x11

However, where the target case uses the stack, the landing pad is elided
due to the presence of a paciasp instruction:

ffff800010032e14:       d503233f        paciasp
ffff800010032e18:       a9bf7bfd        stp     x29, x30, [sp, #-16]!
ffff800010032e1c:       910003fd        mov     x29, sp
ffff800010032e20:       aa0803e0        mov     x0, x8
ffff800010032e24:       940017c0        bl      ffff800010038d24 <kvm_vm_ioctl_check_extension>
ffff800010032e28:       93407c00        sxtw    x0, w0
ffff800010032e2c:       a8c17bfd        ldp     x29, x30, [sp], #16
ffff800010032e30:       d50323bf        autiasp
ffff800010032e34:       d65f03c0        ret

Unfortunately, this results in a fatal exception because paciasp is
compatible only with branch-and-link (call) instructions and not simple
indirect branches.

A fix is being merged into Clang 10.0.1 so that a 'bti j' instruction is
emitted as an explicit landing pad in this situation. Make in-kernel
BTI depend on that compiler version when building with clang.

Cc: Tom Stellard <tstellar@redhat.com>
Cc: Daniel Kiss <daniel.kiss@arm.com>
Reviewed-by: default avatarMark Brown <broonie@kernel.org>
Acked-by: default avatarDave Martin <Dave.Martin@arm.com>
Reviewed-by: default avatarNathan Chancellor <natechancellor@gmail.com>
Acked-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20200615105524.GA2694@willie-the-truck
Link: https://lore.kernel.org/r/20200616183630.2445-1-will@kernel.orgSigned-off-by: default avatarWill Deacon <will@kernel.org>
      b9249cba
  19. 16 Jun, 2020 2 commits
  21. 15 Jun, 2020 5 commits
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