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7c6535c37d
Both GCC [1] and Clang [2] consider the generic version of _THIS_IP_ to
be broken:
#define _THIS_IP_ ({ __label__ __here; __here: (unsigned long)&&__here; })
In particular, the address of a label is only expected to be used with a
computed goto.
While the generic version more or less works today, it is known to be
brittle and may break with current and future optimizations. For
example, Clang -O2 always returns 1 when this function is inlined:
static inline unsigned long get_ip(void)
{ return ({ __label__ __here; __here: (unsigned long)&&__here; }); }
Fix it by overriding _THIS_IP_ in <asm/linkage.h> (which is included by
<linux/instruction_pointer.h>) using an architecture-specific inline asm
version. Additionally, avoiding taking the address of a label prevents
compilers from emitting spurious indirect branch targets (e.g. ENDBR or
BTI) under control-flow integrity schemes.
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120071 [1]
Link: https://github.com/llvm/llvm-project/issues/138272 [2]
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
13 lines
316 B
C
13 lines
316 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __ASM_LINKAGE_H
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#define __ASM_LINKAGE_H
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#include <linux/stringify.h>
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#define __ALIGN .balign CONFIG_FUNCTION_ALIGNMENT, 0x07
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#define __ALIGN_STR __stringify(__ALIGN)
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#define _THIS_IP_ ({ unsigned long __ip; asm volatile("larl %0, ." : "=d" (__ip)); __ip; })
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#endif
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