Discussion:
[PATCH v6 1/2] x86/purgatory: Disable various profiling and sanitizing options
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Hans de Goede
2020-03-17 13:08:40 UTC
Permalink
Since the purgatory is a special stand-alone binary, various profiling
and sanitizing options must be disabled. Having these options enabled
typically will cause dependencies on various special symbols exported by
special libs / stubs used by these frameworks. Since the purgatory is
special, it is not linked against these stubs causing missing symbols in
the purgatory if these options are not disabled.

Sync the set of disabled profiling and sanitizing options with that from
drivers/firmware/efi/libstub/Makefile, adding
-DDISABLE_BRANCH_PROFILING to the CFLAGS and setting:

GCOV_PROFILE := n
UBSAN_SANITIZE := n

This fixes broken references to ftrace_likely_update when
CONFIG_TRACE_BRANCH_PROFILING is enabled and to __gcov_init and
__gcov_exit when CONFIG_GCOV_KERNEL is enabled.

Signed-off-by: Hans de Goede <***@redhat.com>
---
Changes in v6:
- Improve commit message wording
- Rebase on top of tip/master

Changes in v5:
- Not only add -DDISABLE_BRANCH_PROFILING to the CFLAGS but also set:
GCOV_PROFILE := n
UBSAN_SANITIZE := n

Changes in v4:
- This is a new patch in v4 of this series
---
arch/x86/purgatory/Makefile | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 69379bce9574..5313dd7314fe 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -17,9 +17,11 @@ CFLAGS_sha256.o := -D__DISABLE_EXPORTS
LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
targets += purgatory.ro

-# Sanitizer runtimes are unavailable and cannot be linked here.
+# Sanitizer, etc. runtimes are unavailable and cannot be linked here.
+GCOV_PROFILE := n
KASAN_SANITIZE := n
KCSAN_SANITIZE := n
+UBSAN_SANITIZE := n
KCOV_INSTRUMENT := n

# These are adjustments to the compiler flags used for objects that
@@ -27,7 +29,7 @@ KCOV_INSTRUMENT := n

PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
-PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN)
+PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING

# Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
# in turn leaves some undefined symbols like __fentry__ in purgatory and not
--
2.24.1
Hans de Goede
2020-03-17 13:08:41 UTC
Permalink
Linking purgatory.ro with -r enables "incremental linking" this means
no checks for unresolved symbols are done while linking purgatory.ro.

A change to the sha256 code has caused the purgatory in 5.4-rc1 to have
a missing symbol on memzero_explicit, yet things still happily build.

Add an extra check for unresolved symbols by calling ld without -r before
running bin2c to generate kexec-purgatory.c.

This causes a build of 5.4-rc1 with this patch added to fail as it should:

CHK arch/x86/purgatory/purgatory.ro
ld: arch/x86/purgatory/purgatory.ro: in function `sha256_transform':
sha256.c:(.text+0x1c0c): undefined reference to `memzero_explicit'
make[2]: *** [arch/x86/purgatory/Makefile:72:
arch/x86/purgatory/kexec-purgatory.c] Error 1
make[1]: *** [scripts/Makefile.build:509: arch/x86/purgatory] Error 2
make: *** [Makefile:1650: arch/x86] Error 2

Also remove --no-undefined from LDFLAGS_purgatory.ro as that has
no effect.

Signed-off-by: Hans de Goede <***@redhat.com>
---
Changes in v6:
- Improve commit message wording
- Rebase on top of tip/master
---
arch/x86/purgatory/.gitignore | 1 +
arch/x86/purgatory/Makefile | 13 ++++++++++---
2 files changed, 11 insertions(+), 3 deletions(-)
create mode 100644 arch/x86/purgatory/.gitignore

diff --git a/arch/x86/purgatory/.gitignore b/arch/x86/purgatory/.gitignore
new file mode 100644
index 000000000000..d2be1500671d
--- /dev/null
+++ b/arch/x86/purgatory/.gitignore
@@ -0,0 +1 @@
+purgatory.chk
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 5313dd7314fe..679d7dd3024a 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -14,8 +14,12 @@ $(obj)/sha256.o: $(srctree)/lib/crypto/sha256.c FORCE

CFLAGS_sha256.o := -D__DISABLE_EXPORTS

-LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
-targets += purgatory.ro
+# When linking purgatory.ro with -r unresolved symbols are not checked,
+# also link a purgatory.chk binary without -r to check for unresolved symbols.
+PURGATORY_LDFLAGS := -e purgatory_start -nostdlib -z nodefaultlib
+LDFLAGS_purgatory.ro := -r $(PURGATORY_LDFLAGS)
+LDFLAGS_purgatory.chk := $(PURGATORY_LDFLAGS)
+targets += purgatory.ro purgatory.chk

# Sanitizer, etc. runtimes are unavailable and cannot be linked here.
GCOV_PROFILE := n
@@ -62,12 +66,15 @@ CFLAGS_string.o += $(PURGATORY_CFLAGS)
$(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
$(call if_changed,ld)

+$(obj)/purgatory.chk: $(obj)/purgatory.ro FORCE
+ $(call if_changed,ld)
+
targets += kexec-purgatory.c

quiet_cmd_bin2c = BIN2C $@
cmd_bin2c = $(objtree)/scripts/bin2c kexec_purgatory < $< > $@

-$(obj)/kexec-purgatory.c: $(obj)/purgatory.ro FORCE
+$(obj)/kexec-purgatory.c: $(obj)/purgatory.ro $(obj)/purgatory.chk FORCE
$(call if_changed,bin2c)

obj-$(CONFIG_KEXEC_FILE) += kexec-purgatory.o
--
2.24.1
tip-bot2 for Hans de Goede
2020-03-17 22:17:56 UTC
Permalink
The following commit has been merged into the x86/kdump branch of tip:

Commit-ID: e4160b2e4b02377c67f8ecd05786811598f39acd
Gitweb: https://git.kernel.org/tip/e4160b2e4b02377c67f8ecd05786811598f39acd
Author: Hans de Goede <***@redhat.com>
AuthorDate: Tue, 17 Mar 2020 14:08:41 +01:00
Committer: Borislav Petkov <***@suse.de>
CommitterDate: Tue, 17 Mar 2020 15:59:12 +01:00

x86/purgatory: Fail the build if purgatory.ro has missing symbols

Linking purgatory.ro with -r enables "incremental linking"; this means
no checks for unresolved symbols are done while linking purgatory.ro.

A change to the sha256 code has caused the purgatory in 5.4-rc1 to have
a missing symbol on memzero_explicit(), yet things still happily build.

Add an extra check for unresolved symbols by calling ld without -r
before running bin2c to generate kexec-purgatory.c.

This causes a build of 5.4-rc1 with this patch added to fail as it should:

CHK arch/x86/purgatory/purgatory.ro
ld: arch/x86/purgatory/purgatory.ro: in function `sha256_transform':
sha256.c:(.text+0x1c0c): undefined reference to `memzero_explicit'
make[2]: *** [arch/x86/purgatory/Makefile:72:
arch/x86/purgatory/kexec-purgatory.c] Error 1
make[1]: *** [scripts/Makefile.build:509: arch/x86/purgatory] Error 2
make: *** [Makefile:1650: arch/x86] Error 2

Also remove --no-undefined from LDFLAGS_purgatory.ro as that has no
effect.

Signed-off-by: Hans de Goede <***@redhat.com>
Signed-off-by: Borislav Petkov <***@suse.de>
Link: https://lkml.kernel.org/r/20200317130841.290418-2-***@redhat.com
---
arch/x86/purgatory/.gitignore | 1 +
arch/x86/purgatory/Makefile | 13 ++++++++++---
2 files changed, 11 insertions(+), 3 deletions(-)
create mode 100644 arch/x86/purgatory/.gitignore

diff --git a/arch/x86/purgatory/.gitignore b/arch/x86/purgatory/.gitignore
new file mode 100644
index 0000000..d2be150
--- /dev/null
+++ b/arch/x86/purgatory/.gitignore
@@ -0,0 +1 @@
+purgatory.chk
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 9733d1c..54aadbb 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -14,8 +14,12 @@ $(obj)/sha256.o: $(srctree)/lib/crypto/sha256.c FORCE

CFLAGS_sha256.o := -D__DISABLE_EXPORTS

-LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
-targets += purgatory.ro
+# When linking purgatory.ro with -r unresolved symbols are not checked,
+# also link a purgatory.chk binary without -r to check for unresolved symbols.
+PURGATORY_LDFLAGS := -e purgatory_start -nostdlib -z nodefaultlib
+LDFLAGS_purgatory.ro := -r $(PURGATORY_LDFLAGS)
+LDFLAGS_purgatory.chk := $(PURGATORY_LDFLAGS)
+targets += purgatory.ro purgatory.chk

# Sanitizer, etc. runtimes are unavailable and cannot be linked here.
GCOV_PROFILE := n
@@ -61,12 +65,15 @@ CFLAGS_string.o += $(PURGATORY_CFLAGS)
$(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
$(call if_changed,ld)

+$(obj)/purgatory.chk: $(obj)/purgatory.ro FORCE
+ $(call if_changed,ld)
+
targets += kexec-purgatory.c

quiet_cmd_bin2c = BIN2C $@
cmd_bin2c = $(objtree)/scripts/bin2c kexec_purgatory < $< > $@

-$(obj)/kexec-purgatory.c: $(obj)/purgatory.ro FORCE
+$(obj)/kexec-purgatory.c: $(obj)/purgatory.ro $(obj)/purgatory.chk FORCE
$(call if_changed,bin2c)

obj-$(CONFIG_KEXEC_FILE) += kexec-purgatory.o
tip-bot2 for Hans de Goede
2020-03-17 22:17:56 UTC
Permalink
The following commit has been merged into the x86/kdump branch of tip:

Commit-ID: e2ac07c06058ae2d58b45bbf2a2a352771d76fcb
Gitweb: https://git.kernel.org/tip/e2ac07c06058ae2d58b45bbf2a2a352771d76fcb
Author: Hans de Goede <***@redhat.com>
AuthorDate: Tue, 17 Mar 2020 14:08:40 +01:00
Committer: Borislav Petkov <***@suse.de>
CommitterDate: Tue, 17 Mar 2020 15:57:19 +01:00

x86/purgatory: Disable various profiling and sanitizing options

Since the purgatory is a special stand-alone binary, various profiling
and sanitizing options must be disabled. Having these options enabled
typically will cause dependencies on various special symbols exported by
special libs / stubs used by these frameworks. Since the purgatory is
special, it is not linked against these stubs causing missing symbols in
the purgatory if these options are not disabled.

Sync the set of disabled profiling and sanitizing options with that from
drivers/firmware/efi/libstub/Makefile, adding
-DDISABLE_BRANCH_PROFILING to the CFLAGS and setting:

GCOV_PROFILE := n
UBSAN_SANITIZE := n

This fixes broken references to ftrace_likely_update() when
CONFIG_TRACE_BRANCH_PROFILING is enabled and to __gcov_init() and
__gcov_exit() when CONFIG_GCOV_KERNEL is enabled.

Signed-off-by: Hans de Goede <***@redhat.com>
Signed-off-by: Borislav Petkov <***@suse.de>
Link: https://lkml.kernel.org/r/20200317130841.290418-1-***@redhat.com
---
arch/x86/purgatory/Makefile | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index fb4ee54..9733d1c 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -17,7 +17,10 @@ CFLAGS_sha256.o := -D__DISABLE_EXPORTS
LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
targets += purgatory.ro

+# Sanitizer, etc. runtimes are unavailable and cannot be linked here.
+GCOV_PROFILE := n
KASAN_SANITIZE := n
+UBSAN_SANITIZE := n
KCOV_INSTRUMENT := n

# These are adjustments to the compiler flags used for objects that
@@ -25,7 +28,7 @@ KCOV_INSTRUMENT := n

PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
-PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN)
+PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING

# Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
# in turn leaves some undefined symbols like __fentry__ in purgatory and not
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