Commit 0138ba5783ae ("powerpc/64/signal: Balance return predictor
stack in signal trampoline") changed __kernel_sigtramp_rt64() VDSO and
trampoline code, and introduced a regression in the way glibc's
backtrace()[1] detects the signal-handler stack frame. Apart from the
practical implications, __kernel_sigtramp_rt64() was a VDSO function
with the semantics that it is a function you can call from userspace
to end a signal handling. Now this semantics are no longer valid.

I believe the aforementioned change affects all releases since 5.9.

This patch tries to fix both the semantics and practical aspect of
__kernel_sigtramp_rt64() returning it to the previous code, whilst
keeping the intended behaviour of 0138ba5783ae by adding a new symbol
to serve as the jump target from the kernel to the trampoline. Now the
trampoline has two parts, a new entry point and the old return point.

[1] https://lists.ozlabs.org/pipermail/linuxppc-dev/2021-January/223194.html

Fixes: 0138ba5783ae ("powerpc/64/signal: Balance return predictor stack in signal trampoline")
Cc: stable@vger.kernel.org # v5.9+
Signed-off-by: Raoni Fassina Firmino <raoni@linux.ibm.com>
Acked-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Minor tweaks to change log formatting, add stable tag]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210201200505.iz46ubcizipnkcxe@work-tp

VDSO64 is only built for the 64-bit kernel, hence vgettimeofday.o is
built by the generic rule in scripts/Makefile.build.

This line does not provide anything useful.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201223171142.707053-2-masahiroy@kernel.org

vgettimeofday.o is unnecessarily rebuilt. Adding it to 'targets' is not
enough to fix the issue. Kbuild is correctly rebuilding it because the
command line is changed.

PowerPC builds each vdso directory twice; first in vdso_prepare to
generate vdso{32,64}-offsets.h, second as part of the ordinary build
process to embed vdso{32,64}.so.dbg into the kernel.

The problem shows up when CONFIG_PPC_WERROR=y due to the following line
in arch/powerpc/Kbuild:

  subdir-ccflags-$(CONFIG_PPC_WERROR) := -Werror

In the preparation stage, Kbuild directly visits the vdso directories,
hence it does not inherit subdir-ccflags-y. In the second descend,
Kbuild adds -Werror, which results in the command line flipping
with/without -Werror.

It implies a potential danger; if a more critical flag that would impact
the resulted vdso, the offsets recorded in the headers might be different
from real offsets in the embedded vdso images.

Removing the unneeded second descend solves the problem.

Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/linuxppc-dev/87tuslxhry.fsf@mpe.ellerman.id.au/
Link: https://lore.kernel.org/r/20201223171142.707053-1-masahiroy@kernel.org

Add R_PPC_REL24 relocations to the list of relocations we do NOT
support in the VDSO.

These are generated in some cases and we do not support relocating
them at runtime, so if they appear then the VDSO will not work at
runtime, therefore it's preferable to break the build if we see them.

Fixes: ab037dd87a2f ("powerpc/vdso: Switch VDSO to generic C implementation.")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201218111619.1206391-1-mpe@ellerman.id.au

Use the common STABS_DEBUG and DWARF_DEBUG and ELF_DETAILS macro rule for
the linker script in an effort.

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1606460857-2723-1-git-send-email-tangyouling@loongson.cn

VDSO32_LBASE and VDSO64_LBASE are 0. Remove them to simplify code.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/6c4d6570d886bbe1cc471e8ca01602e4b4d9beb5.1601197618.git.christophe.leroy@csgroup.eu

__kernel_datapage_offset is not used anymore, remove it.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/ddb5c746bec4e1a026d7c85243213a1876ef844f.1601197618.git.christophe.leroy@csgroup.eu

__kernel_sync_dicache_p5() is an alternative to
__kernel_sync_dicache() when cpu has CPU_FTR_COHERENT_ICACHE

Remove this alternative function and merge
__kernel_sync_dicache_p5() into __kernel_sync_dicache() using
standard CPU feature fixup.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/4c7dcc6544882761b2b0249d7a8ec2c3a8088cb5.1601197618.git.christophe.leroy@csgroup.eu

Add builtin symbols to locate fixup section and use them
instead of locating sections through elf headers at runtime.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/2954526981859ca1ccfcfc7a7c4263920e9ddfcb.1601197618.git.christophe.leroy@csgroup.eu

This is copied from arm64.

Instead of using runtime generated signal trampoline offsets,
get offsets at buildtime.

If the said trampoline doesn't exist, build will fail. So no
need to check whether the trampoline exists or not in the VDSO.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/f8bfd6812c3e3678b1cdb4d55a52f9eb022b40d3.1601197618.git.christophe.leroy@csgroup.eu