fe8c8a1268
Disabling compiler optimizations can be fragile, since a new optimization could be added to -O0 or -Os that breaks the assumptions the code is making. Instead of disabling compiler optimizations, use a dummy inline assembly (based on RELOC_HIDE) to block the problematic kinds of optimization, while still allowing other optimizations to be applied to the code. The dummy inline assembly is added after every OR, and has the accumulator variable as its input and output. The compiler is forced to assume that the dummy inline assembly could both depend on the accumulator variable and change the accumulator variable, so it is forced to compute the value correctly before the inline assembly, and cannot assume anything about its value after the inline assembly. This change should be enough to make crypto_memneq work correctly (with data-independent timing) even if it is inlined at its call sites. That can be done later in a followup patch. Compile-tested on x86_64. Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.eti.br> Acked-by: Daniel Borkmann <dborkman@redhat.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
118 lines
4.1 KiB
C
118 lines
4.1 KiB
C
#ifndef __LINUX_COMPILER_H
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#error "Please don't include <linux/compiler-gcc.h> directly, include <linux/compiler.h> instead."
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#endif
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/*
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* Common definitions for all gcc versions go here.
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*/
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#define GCC_VERSION (__GNUC__ * 10000 \
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+ __GNUC_MINOR__ * 100 \
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+ __GNUC_PATCHLEVEL__)
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/* Optimization barrier */
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/* The "volatile" is due to gcc bugs */
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#define barrier() __asm__ __volatile__("": : :"memory")
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/*
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* This macro obfuscates arithmetic on a variable address so that gcc
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* shouldn't recognize the original var, and make assumptions about it.
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*
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* This is needed because the C standard makes it undefined to do
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* pointer arithmetic on "objects" outside their boundaries and the
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* gcc optimizers assume this is the case. In particular they
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* assume such arithmetic does not wrap.
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*
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* A miscompilation has been observed because of this on PPC.
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* To work around it we hide the relationship of the pointer and the object
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* using this macro.
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*
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* Versions of the ppc64 compiler before 4.1 had a bug where use of
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* RELOC_HIDE could trash r30. The bug can be worked around by changing
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* the inline assembly constraint from =g to =r, in this particular
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* case either is valid.
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*/
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#define RELOC_HIDE(ptr, off) \
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({ unsigned long __ptr; \
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__asm__ ("" : "=r"(__ptr) : "0"(ptr)); \
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(typeof(ptr)) (__ptr + (off)); })
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/* Make the optimizer believe the variable can be manipulated arbitrarily. */
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#define OPTIMIZER_HIDE_VAR(var) __asm__ ("" : "=r" (var) : "0" (var))
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#ifdef __CHECKER__
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#define __must_be_array(arr) 0
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#else
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/* &a[0] degrades to a pointer: a different type from an array */
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#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
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#endif
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/*
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* Force always-inline if the user requests it so via the .config,
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* or if gcc is too old:
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*/
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#if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \
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!defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4)
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# define inline inline __attribute__((always_inline)) notrace
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# define __inline__ __inline__ __attribute__((always_inline)) notrace
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# define __inline __inline __attribute__((always_inline)) notrace
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#else
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/* A lot of inline functions can cause havoc with function tracing */
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# define inline inline notrace
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# define __inline__ __inline__ notrace
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# define __inline __inline notrace
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#endif
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#define __deprecated __attribute__((deprecated))
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#define __packed __attribute__((packed))
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#define __weak __attribute__((weak))
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/*
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* it doesn't make sense on ARM (currently the only user of __naked) to trace
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* naked functions because then mcount is called without stack and frame pointer
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* being set up and there is no chance to restore the lr register to the value
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* before mcount was called.
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*
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* The asm() bodies of naked functions often depend on standard calling conventions,
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* therefore they must be noinline and noclone. GCC 4.[56] currently fail to enforce
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* this, so we must do so ourselves. See GCC PR44290.
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*/
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#define __naked __attribute__((naked)) noinline __noclone notrace
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#define __noreturn __attribute__((noreturn))
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/*
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* From the GCC manual:
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*
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* Many functions have no effects except the return value and their
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* return value depends only on the parameters and/or global
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* variables. Such a function can be subject to common subexpression
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* elimination and loop optimization just as an arithmetic operator
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* would be.
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* [...]
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*/
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#define __pure __attribute__((pure))
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#define __aligned(x) __attribute__((aligned(x)))
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#define __printf(a, b) __attribute__((format(printf, a, b)))
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#define __scanf(a, b) __attribute__((format(scanf, a, b)))
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#define noinline __attribute__((noinline))
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#define __attribute_const__ __attribute__((__const__))
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#define __maybe_unused __attribute__((unused))
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#define __always_unused __attribute__((unused))
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#define __gcc_header(x) #x
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#define _gcc_header(x) __gcc_header(linux/compiler-gcc##x.h)
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#define gcc_header(x) _gcc_header(x)
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#include gcc_header(__GNUC__)
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#if !defined(__noclone)
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#define __noclone /* not needed */
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#endif
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/*
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* A trick to suppress uninitialized variable warning without generating any
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* code
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*/
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#define uninitialized_var(x) x = x
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#define __always_inline inline __attribute__((always_inline))
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