Re: [PATCH] STACK_PROTECTOR: Support symbols emitted by windows compiler

[Daniel Kiper]

Adding Ard, Glenn and Dave...

First of all, sorry for late reply but I was busy with other stuff...

On Fri, Mar 15, 2024 at 09:43:22PM +0300, Vladimir 'phcoder' Serbinenko wrote:
> stack protector needs symbols with just one underscore in C
> name unlike unix variant that needs double underscore.
> Supply both symbols for simplicity
>
> Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>

I do not like your solution because it adds unneeded code/symbols to
some EFI builds. I come up with two other solutions.

First, let's define an alias when using MinGW build environment:

diff --git a/include/grub/stack_protector.h b/include/grub/stack_protector.h
index c88dc00b5..8d99fd50e 100644
--- a/include/grub/stack_protector.h
+++ b/include/grub/stack_protector.h
@@ -25,6 +25,10 @@
 #ifdef GRUB_STACK_PROTECTOR
 extern grub_addr_t EXPORT_VAR (__stack_chk_guard);
 extern void __attribute__ ((noreturn)) EXPORT_FUNC (__stack_chk_fail) (void);
+#if defined(_WIN32) && !defined(__CYGWIN__)
+static grub_addr_t __attribute__ ((weakref("__stack_chk_guard"))) EXPORT_VAR 
(_stack_chk_guard);
+static void __attribute__ ((noreturn, weakref("__stack_chk_fail"))) 
EXPORT_FUNC (_stack_chk_fail) (void);
+#endif
 #endif

 #endif /* GRUB_STACK_PROTECTOR_H */

Tested and it works. We have to use weakref() instead of alias() due to
definition in separate translation unit.

Second, do not drop leading underscore:

diff --git a/conf/Makefile.common b/conf/Makefile.common
index b8f216f6c..fd20f6b4e 100644
--- a/conf/Makefile.common
+++ b/conf/Makefile.common
@@ -38,7 +38,7 @@ CCASFLAGS_DEFAULT = $(CPPFLAGS_DEFAULT) -DASM_FILE=1
 BUILD_CPPFLAGS += $(CPPFLAGS_DEFAULT)

 CFLAGS_KERNEL = $(CFLAGS_PLATFORM) -ffreestanding
-LDFLAGS_KERNEL = $(LDFLAGS_PLATFORM) -nostdlib $(TARGET_LDFLAGS_OLDMAGIC)
+LDFLAGS_KERNEL = $(LDFLAGS_PLATFORM) -nostdlib $(TARGET_LDFLAGS_OLDMAGIC) 
-Wl,--leading-underscore
 CPPFLAGS_KERNEL = $(CPPFLAGS_CPU) $(CPPFLAGS_PLATFORM) -DGRUB_KERNEL=1
 CCASFLAGS_KERNEL = $(CCASFLAGS_CPU) $(CCASFLAGS_PLATFORM)
 STRIPFLAGS_KERNEL = -R .rel.dyn -R .reginfo -R .note -R .comment -R .drectve 
-R .note.gnu.gold-version -R .MIPS.abiflags -R .ARM.exidx
@@ -51,12 +51,12 @@ endif
 endif

 CFLAGS_MODULE = $(CFLAGS_PLATFORM) -ffreestanding
-LDFLAGS_MODULE = $(LDFLAGS_PLATFORM) -nostdlib $(TARGET_LDFLAGS_OLDMAGIC) 
-Wl,-r
+LDFLAGS_MODULE = $(LDFLAGS_PLATFORM) -nostdlib $(TARGET_LDFLAGS_OLDMAGIC) 
-Wl,-r -Wl,--leading-underscore
 CPPFLAGS_MODULE = $(CPPFLAGS_CPU) $(CPPFLAGS_PLATFORM)
 CCASFLAGS_MODULE = $(CCASFLAGS_CPU) $(CCASFLAGS_PLATFORM)

 CFLAGS_IMAGE = $(CFLAGS_PLATFORM) -fno-builtin
-LDFLAGS_IMAGE = $(LDFLAGS_PLATFORM) -nostdlib $(TARGET_LDFLAGS_OLDMAGIC) -Wl,-S
+LDFLAGS_IMAGE = $(LDFLAGS_PLATFORM) -nostdlib $(TARGET_LDFLAGS_OLDMAGIC) 
-Wl,-S -Wl,--leading-underscore
 CPPFLAGS_IMAGE = $(CPPFLAGS_CPU) $(CPPFLAGS_PLATFORM)
 CCASFLAGS_IMAGE = $(CCASFLAGS_CPU) $(CCASFLAGS_PLATFORM)

diff --git a/grub-core/genmod.sh.in b/grub-core/genmod.sh.in
index e57c4d920..04b680ad0 100644
--- a/grub-core/genmod.sh.in
+++ b/grub-core/genmod.sh.in
@@ -83,9 +83,9 @@ else
     for dep in $deps; do echo "char moddep_$dep[] __attribute__ 
((section(\"_moddeps, _moddeps\"))) = \"$dep\";" >>$t2; done

     if test -n "$deps"; then
-       @TARGET_CC@ @TARGET_LDFLAGS@ -ffreestanding -nostdlib -o $tmpfile2 $t1 
$t2 $tmpfile -Wl,-r
+       @TARGET_CC@ @TARGET_LDFLAGS@ -ffreestanding -nostdlib 
-Wl,--leading-underscore -o $tmpfile2 $t1 $t2 $tmpfile -Wl,-r
     else
-       @TARGET_CC@ @TARGET_LDFLAGS@ -ffreestanding -nostdlib -o $tmpfile2 $t1 
$tmpfile -Wl,-r
+       @TARGET_CC@ @TARGET_LDFLAGS@ -ffreestanding -nostdlib 
-Wl,--leading-underscore -o $tmpfile2 $t1 $tmpfile -Wl,-r
     fi
     rm -f $t1 $t2 $tmpfile
     mv $tmpfile2 $tmpfile
diff --git a/util/grub-pe2elf.c b/util/grub-pe2elf.c
index 11331294f..233118252 100644
--- a/util/grub-pe2elf.c
+++ b/util/grub-pe2elf.c
@@ -71,7 +71,7 @@ insert_string (const char *name)
 {
   int len, result;

-  if (*name == '_')
+  if (*name == '_' && !strcmp("__stack_chk_fail", name) && 
!strcmp("__stack_chk_guard", name))
     name++;

   len = strlen (name);

This one works too. However, it breaks normal builds. So, it requires some
tweaking to make it production ready.

Anyway, I prefer first solution because it is simpler. I do not mention
that the second one may break other symbols with leading underscore.

What do you think?

Daniel