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Commit 3dd518cb authored by Zhenzhong Duan's avatar Zhenzhong Duan Committed by Greg Kroah-Hartman
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x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support 



commit 4cd24de3a0980bf3100c9dcb08ef65ca7c31af48 upstream.

Since retpoline capable compilers are widely available, make
CONFIG_RETPOLINE hard depend on the compiler capability.

Break the build when CONFIG_RETPOLINE is enabled and the compiler does not
support it. Emit an error message in that case:

 "arch/x86/Makefile:226: *** You are building kernel with non-retpoline
  compiler, please update your compiler..  Stop."

[dwmw: Fail the build with non-retpoline compiler]

Suggested-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarZhenzhong Duan <zhenzhong.duan@oracle.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Borislav Petkov <bp@suse.de>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: <srinivas.eeda@oracle.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/cca0cb20-f9e2-4094-840b-fb0f8810cd34@default


[bwh: Backported to 4.9:
 - Drop change to objtool options
 - Adjust context, indentation]
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 890fb470

arch/x86/Kconfig

+0 −4
Original line number Diff line number Diff line
@@ -418,10 +418,6 @@ config RETPOLINE 
	  branches. Requires a compiler with -mindirect-branch=thunk-extern

	  support for full protection. The kernel may run slower.



	  Without compiler support, at least indirect branches in assembler

	  code are eliminated. Since this includes the syscall entry path,

	  it is not entirely pointless.



if X86_32

config X86_EXTENDED_PLATFORM

	bool "Support for extended (non-PC) x86 platforms"

arch/x86/Makefile

+3 −2
Original line number Diff line number Diff line
@@ -221,9 +221,10 @@ ifdef CONFIG_RETPOLINE 
    RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk



    RETPOLINE_CFLAGS += $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG)))

    ifneq ($(RETPOLINE_CFLAGS),)

        KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DRETPOLINE

    ifeq ($(RETPOLINE_CFLAGS),)

      $(error You are building kernel with non-retpoline compiler, please update your compiler.)

    endif

    KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)

endif



archscripts: scripts_basic

arch/x86/include/asm/nospec-branch.h

+6 −4
Original line number Diff line number Diff line
@@ -164,11 +164,12 @@ 
	_ASM_PTR " 999b\n\t"					\

	".popsection\n\t"



#if defined(CONFIG_X86_64) && defined(RETPOLINE)

#ifdef CONFIG_RETPOLINE

#ifdef CONFIG_X86_64



/*

 * Since the inline asm uses the %V modifier which is only in newer GCC,

 * the 64-bit one is dependent on RETPOLINE not CONFIG_RETPOLINE.

 * Inline asm uses the %V modifier which is only in newer GCC

 * which is ensured when CONFIG_RETPOLINE is defined.

 */

# define CALL_NOSPEC						\

	ANNOTATE_NOSPEC_ALTERNATIVE				\
@@ -183,7 +184,7 @@ 
	X86_FEATURE_RETPOLINE_AMD)

# define THUNK_TARGET(addr) [thunk_target] "r" (addr)



#elif defined(CONFIG_X86_32) && defined(CONFIG_RETPOLINE)

#else /* CONFIG_X86_32 */

/*

 * For i386 we use the original ret-equivalent retpoline, because

 * otherwise we'll run out of registers. We don't care about CET
@@ -213,6 +214,7 @@ 
	X86_FEATURE_RETPOLINE_AMD)



# define THUNK_TARGET(addr) [thunk_target] "rm" (addr)

#endif

#else /* No retpoline for C / inline asm */

# define CALL_NOSPEC "call *%[thunk_target]\n"

# define THUNK_TARGET(addr) [thunk_target] "rm" (addr)

arch/x86/kernel/cpu/bugs.c

+1 −1
Original line number Diff line number Diff line
@@ -812,7 +812,7 @@ static void __init spec_v2_print_cond(const char *reason, bool secure) 


static inline bool retp_compiler(void)

{

	return __is_defined(RETPOLINE);

	return __is_defined(CONFIG_RETPOLINE);

}



static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)