Commit 3347acc6 authored by Arvind Sankar's avatar Arvind Sankar Committed by Linus Torvalds
Browse files

compiler.h: fix barrier_data() on clang 

Commit 815f0ddb ("include/linux/compiler*.h: make compiler-*.h
mutually exclusive") neglected to copy barrier_data() from
compiler-gcc.h into compiler-clang.h.

The definition in compiler-gcc.h was really to work around clang's more
aggressive optimization, so this broke barrier_data() on clang, and
consequently memzero_explicit() as well.

For example, this results in at least the memzero_explicit() call in
lib/crypto/sha256.c:sha256_transform() being optimized away by clang.

Fix this by moving the definition of barrier_data() into compiler.h.

Also move the gcc/clang definition of barrier() into compiler.h,
__memory_barrier() is icc-specific (and barrier() is already defined
using it in compiler-intel.h) and doesn't belong in compiler.h.

[rdunlap@infradead.org: fix ALPHA builds when SMP is not enabled]

Link: https://lkml.kernel.org/r/20201101231835.4589-1-rdunlap@infradead.org


Fixes: 815f0ddb ("include/linux/compiler*.h: make compiler-*.h mutually exclusive")
Signed-off-by: default avatarArvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: default avatarRandy Dunlap <rdunlap@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Tested-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Reviewed-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201014212631.207844-1-nivedita@alum.mit.edu


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 96e1fac1

include/asm-generic/barrier.h

+1 −0
Original line number Diff line number Diff line
@@ -13,6 +13,7 @@ 


#ifndef __ASSEMBLY__



#include <linux/compiler.h>

#include <asm/rwonce.h>



#ifndef nop

include/linux/compiler-clang.h

+0 −6
Original line number Diff line number Diff line
@@ -60,12 +60,6 @@ 
#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1

#endif



/* The following are for compatibility with GCC, from compiler-gcc.h,

 * and may be redefined here because they should not be shared with other

 * compilers, like ICC.

 */

#define barrier() __asm__ __volatile__("" : : : "memory")



#if __has_feature(shadow_call_stack)

# define __noscs	__attribute__((__no_sanitize__("shadow-call-stack")))

#endif

include/linux/compiler-gcc.h

+0 −19
Original line number Diff line number Diff line
@@ -15,25 +15,6 @@ 
# error Sorry, your version of GCC is too old - please use 4.9 or newer.

#endif



/* Optimization barrier */



/* The "volatile" is due to gcc bugs */

#define barrier() __asm__ __volatile__("": : :"memory")

/*

 * This version is i.e. to prevent dead stores elimination on @ptr

 * where gcc and llvm may behave differently when otherwise using

 * normal barrier(): while gcc behavior gets along with a normal

 * barrier(), llvm needs an explicit input variable to be assumed

 * clobbered. The issue is as follows: while the inline asm might

 * access any memory it wants, the compiler could have fit all of

 * @ptr into memory registers instead, and since @ptr never escaped

 * from that, it proved that the inline asm wasn't touching any of

 * it. This version works well with both compilers, i.e. we're telling

 * the compiler that the inline asm absolutely may see the contents

 * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495

 */

#define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory")



/*

 * This macro obfuscates arithmetic on a variable address so that gcc

 * shouldn't recognize the original var, and make assumptions about it.

include/linux/compiler.h

+16 −2
Original line number Diff line number Diff line
@@ -80,11 +80,25 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, 


/* Optimization barrier */

#ifndef barrier

# define barrier() __memory_barrier()

/* The "volatile" is due to gcc bugs */

# define barrier() __asm__ __volatile__("": : :"memory")

#endif



#ifndef barrier_data

# define barrier_data(ptr) barrier()

/*

 * This version is i.e. to prevent dead stores elimination on @ptr

 * where gcc and llvm may behave differently when otherwise using

 * normal barrier(): while gcc behavior gets along with a normal

 * barrier(), llvm needs an explicit input variable to be assumed

 * clobbered. The issue is as follows: while the inline asm might

 * access any memory it wants, the compiler could have fit all of

 * @ptr into memory registers instead, and since @ptr never escaped

 * from that, it proved that the inline asm wasn't touching any of

 * it. This version works well with both compilers, i.e. we're telling

 * the compiler that the inline asm absolutely may see the contents

 * of @ptr. See also: https://llvm.org/bugs/show_bug.cgi?id=15495

 */

# define barrier_data(ptr) __asm__ __volatile__("": :"r"(ptr) :"memory")

#endif



/* workaround for GCC PR82365 if needed */

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