Commit 514ca14e authored by ndesaulniers@google.com's avatar ndesaulniers@google.com Committed by Josh Poimboeuf
Browse files

start_kernel: Add __no_stack_protector function attribute 

Back during the discussion of
commit a9a3ed1e ("x86: Fix early boot crash on gcc-10, third try")
we discussed the need for a function attribute to control the omission
of stack protectors on a per-function basis; at the time Clang had
support for no_stack_protector but GCC did not. This was fixed in
gcc-11. Now that the function attribute is available, let's start using
it.

Callers of boot_init_stack_canary need to use this function attribute
unless they're compiled with -fno-stack-protector, otherwise the canary
stored in the stack slot of the caller will differ upon the call to
boot_init_stack_canary. This will lead to a call to __stack_chk_fail()
then panic.

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94722
Link: https://lore.kernel.org/all/20200316130414.GC12561@hirez.programming.kicks-ass.net/


Tested-by: default avatarNathan Chancellor <nathan@kernel.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Acked-by: default avatarMiguel Ojeda <ojeda@kernel.org>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20230412-no_stackp-v2-1-116f9fe4bbe7@google.com


Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>

Signed-off-by: default avatarndesaulniers@google.com <ndesaulniers@google.com>
parent 95f0e3a2

arch/powerpc/kernel/smp.c

+1 −0
Original line number Diff line number Diff line
@@ -1605,6 +1605,7 @@ static void add_cpu_to_masks(int cpu) 
}



/* Activate a secondary processor. */

__no_stack_protector

void start_secondary(void *unused)

{

	unsigned int cpu = raw_smp_processor_id();

include/linux/compiler_attributes.h

+12 −0
Original line number Diff line number Diff line
@@ -255,6 +255,18 @@ 
 */

#define __noreturn                      __attribute__((__noreturn__))



/*

 * Optional: only supported since GCC >= 11.1, clang >= 7.0.

 *

 *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-no_005fstack_005fprotector-function-attribute

 *   clang: https://clang.llvm.org/docs/AttributeReference.html#no-stack-protector-safebuffers

 */

#if __has_attribute(__no_stack_protector__)

# define __no_stack_protector		__attribute__((__no_stack_protector__))

#else

# define __no_stack_protector

#endif



/*

 * Optional: not supported by gcc.

 *

init/main.c

+2 −1
Original line number Diff line number Diff line
@@ -877,7 +877,8 @@ static void __init print_unknown_bootoptions(void) 
	memblock_free(unknown_options, len);

}



asmlinkage __visible void __init __no_sanitize_address __noreturn start_kernel(void)

asmlinkage __visible __init __no_sanitize_address __noreturn __no_stack_protector

void start_kernel(void)

{

	char *command_line;

	char *after_dashes;