From 76366050eb1b3151c4b4110c76538ff14dffb74c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20D=C3=ADaz?= <daniel.diaz@linaro.org>
Date: Wed, 19 Aug 2020 12:32:24 -0500
Subject: [PATCH 1/3] x86/defconfigs: Explicitly unset CONFIG_64BIT in
i386_defconfig
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
A recent refresh of the defconfigs got rid of the following
(unset) config:
# CONFIG_64BIT is not set
Innocuous as it seems, when the config file is saved again the
behavior is changed so that CONFIG_64BIT=y.
Currently,
$ make i386_defconfig
$ grep CONFIG_64BIT .config
CONFIG_64BIT=y
whereas previously (and with this patch):
$ make i386_defconfig
$ grep CONFIG_64BIT .config
# CONFIG_64BIT is not set
( This was found with weird compiler errors on OpenEmbedded
builds, as the compiler was unable to cope with 64-bits data
types. )
Fixes: 1d0e12fd3a84 ("x86/defconfigs: Refresh defconfig files")
Reported-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Daniel Díaz <daniel.diaz@linaro.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/configs/i386_defconfig | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/x86/configs/i386_defconfig b/arch/x86/configs/i386_defconfig
index d7577fece9eb..4cfdf5755ab5 100644
--- a/arch/x86/configs/i386_defconfig
+++ b/arch/x86/configs/i386_defconfig
@@ -19,6 +19,7 @@ CONFIG_CGROUP_CPUACCT=y
CONFIG_BLK_DEV_INITRD=y
# CONFIG_COMPAT_BRK is not set
CONFIG_PROFILING=y
+# CONFIG_64BIT is not set
CONFIG_SMP=y
CONFIG_X86_GENERIC=y
CONFIG_HPET_TIMER=y
From 09e43968db40c33a73e9ddbfd937f46d5c334924 Mon Sep 17 00:00:00 2001
From: Arvind Sankar <nivedita@alum.mit.edu>
Date: Tue, 11 Aug 2020 20:43:08 -0400
Subject: [PATCH 2/3] x86/boot/compressed: Disable relocation relaxation
The x86-64 psABI [0] specifies special relocation types
(R_X86_64_[REX_]GOTPCRELX) for indirection through the Global Offset
Table, semantically equivalent to R_X86_64_GOTPCREL, which the linker
can take advantage of for optimization (relaxation) at link time. This
is supported by LLD and binutils versions 2.26 onwards.
The compressed kernel is position-independent code, however, when using
LLD or binutils versions before 2.27, it must be linked without the -pie
option. In this case, the linker may optimize certain instructions into
a non-position-independent form, by converting foo@GOTPCREL(%rip) to $foo.
This potential issue has been present with LLD and binutils-2.26 for a
long time, but it has never manifested itself before now:
- LLD and binutils-2.26 only relax
movq foo@GOTPCREL(%rip), %reg
to
leaq foo(%rip), %reg
which is still position-independent, rather than
mov $foo, %reg
which is permitted by the psABI when -pie is not enabled.
- GCC happens to only generate GOTPCREL relocations on mov instructions.
- CLang does generate GOTPCREL relocations on non-mov instructions, but
when building the compressed kernel, it uses its integrated assembler
(due to the redefinition of KBUILD_CFLAGS dropping -no-integrated-as),
which has so far defaulted to not generating the GOTPCRELX
relocations.
Nick Desaulniers reports [1,2]:
"A recent change [3] to a default value of configuration variable
(ENABLE_X86_RELAX_RELOCATIONS OFF -> ON) in LLVM now causes Clang's
integrated assembler to emit R_X86_64_GOTPCRELX/R_X86_64_REX_GOTPCRELX
relocations. LLD will relax instructions with these relocations based
on whether the image is being linked as position independent or not.
When not, then LLD will relax these instructions to use absolute
addressing mode (R_RELAX_GOT_PC_NOPIC). This causes kernels built with
Clang and linked with LLD to fail to boot."
Patch series [4] is a solution to allow the compressed kernel to be
linked with -pie unconditionally, but even if merged is unlikely to be
backported. As a simple solution that can be applied to stable as well,
prevent the assembler from generating the relaxed relocation types using
the -mrelax-relocations=no option. For ease of backporting, do this
unconditionally.
[0] https://gitlab.com/x86-psABIs/x86-64-ABI/-/blob/master/x86-64-ABI/linker-optimization.tex#L65
[1] https://lore.kernel.org/lkml/20200807194100.3570838-1-ndesaulniers@google.com/
[2] https://github.com/ClangBuiltLinux/linux/issues/1121
[3] https://reviews.llvm.org/rGc41a18cf61790fc898dcda1055c3efbf442c14c0
[4] https://lore.kernel.org/lkml/20200731202738.2577854-1-nivedita@alum.mit.edu/
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200812004308.1448603-1-nivedita@alum.mit.edu
---
arch/x86/boot/compressed/Makefile | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 3962f592633d..ff7894f39e0e 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -43,6 +43,8 @@ KBUILD_CFLAGS += -Wno-pointer-sign
KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
KBUILD_CFLAGS += -D__DISABLE_EXPORTS
+# Disable relocation relaxation in case the link is not PIE.
+KBUILD_CFLAGS += $(call as-option,-Wa$(comma)-mrelax-relocations=no)
KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
GCOV_PROFILE := n
From 6f9885a36c006d798319661fa849f9c2922223b9 Mon Sep 17 00:00:00 2001
From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Mon, 14 Sep 2020 12:04:22 -0500
Subject: [PATCH 3/3] x86/unwind/fp: Fix FP unwinding in ret_from_fork
There have been some reports of "bad bp value" warnings printed by the
frame pointer unwinder:
WARNING: kernel stack regs at 000000005bac7112 in sh:1014 has bad 'bp' value 0000000000000000
This warning happens when unwinding from an interrupt in
ret_from_fork(). If entry code gets interrupted, the state of the
frame pointer (rbp) may be undefined, which can confuse the unwinder,
resulting in warnings like the above.
There's an in_entry_code() check which normally silences such
warnings for entry code. But in this case, ret_from_fork() is getting
interrupted. It recently got moved out of .entry.text, so the
in_entry_code() check no longer works.
It could be moved back into .entry.text, but that would break the
noinstr validation because of the call to schedule_tail().
Instead, initialize each new task's RBP to point to the task's entry
regs via an encoded frame pointer. That will allow the unwinder to
reach the end of the stack gracefully.
Fixes: b9f6976bfb94 ("x86/entry/64: Move non entry code into .text section")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/f366bbf5a8d02e2318ee312f738112d0af74d16f.1600103007.git.jpoimboe@redhat.com
---
arch/x86/include/asm/frame.h | 19 +++++++++++++++++++
arch/x86/kernel/process.c | 3 ++-
2 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/frame.h b/arch/x86/include/asm/frame.h
index 296b346184b2..fb42659f6e98 100644
--- a/arch/x86/include/asm/frame.h
+++ b/arch/x86/include/asm/frame.h
@@ -60,12 +60,26 @@
#define FRAME_END "pop %" _ASM_BP "\n"
#ifdef CONFIG_X86_64
+
#define ENCODE_FRAME_POINTER \
"lea 1(%rsp), %rbp\n\t"
+
+static inline unsigned long encode_frame_pointer(struct pt_regs *regs)
+{
+ return (unsigned long)regs + 1;
+}
+
#else /* !CONFIG_X86_64 */
+
#define ENCODE_FRAME_POINTER \
"movl %esp, %ebp\n\t" \
"andl $0x7fffffff, %ebp\n\t"
+
+static inline unsigned long encode_frame_pointer(struct pt_regs *regs)
+{
+ return (unsigned long)regs & 0x7fffffff;
+}
+
#endif /* CONFIG_X86_64 */
#endif /* __ASSEMBLY__ */
@@ -83,6 +97,11 @@
#define ENCODE_FRAME_POINTER
+static inline unsigned long encode_frame_pointer(struct pt_regs *regs)
+{
+ return 0;
+}
+
#endif
#define FRAME_BEGIN
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 13ce616cc7af..ba4593a913fa 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -42,6 +42,7 @@
#include <asm/spec-ctrl.h>
#include <asm/io_bitmap.h>
#include <asm/proto.h>
+#include <asm/frame.h>
#include "process.h"
@@ -133,7 +134,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, unsigned long arg,
fork_frame = container_of(childregs, struct fork_frame, regs);
frame = &fork_frame->frame;
- frame->bp = 0;
+ frame->bp = encode_frame_pointer(childregs);
frame->ret_addr = (unsigned long) ret_from_fork;
p->thread.sp = (unsigned long) fork_frame;
p->thread.io_bitmap = NULL;