path: root/arch/s390/include/asm/nospec-branch.h
diff options
authorMartin Schwidefsky <schwidefsky@de.ibm.com>2018-01-26 12:46:47 +0100
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2018-02-07 15:57:02 +0100
commitf19fbd5ed642dc31c809596412dab1ed56f2f156 (patch)
treeb1ef7f48d102801d718baab1ae4cec2588cc5862 /arch/s390/include/asm/nospec-branch.h
parent6b73044b2b0081ee3dd1cd6eaab7dee552601efb (diff)
s390: introduce execute-trampolines for branches
Add CONFIG_EXPOLINE to enable the use of the new -mindirect-branch= and -mfunction_return= compiler options to create a kernel fortified against the specte v2 attack. With CONFIG_EXPOLINE=y all indirect branches will be issued with an execute type instruction. For z10 or newer the EXRL instruction will be used, for older machines the EX instruction. The typical indirect call basr %r14,%r1 is replaced with a PC relative call to a new thunk brasl %r14,__s390x_indirect_jump_r1 The thunk contains the EXRL/EX instruction to the indirect branch __s390x_indirect_jump_r1: exrl 0,0f j . 0: br %r1 The detour via the execute type instruction has a performance impact. To get rid of the detour the new kernel parameter "nospectre_v2" and "spectre_v2=[on,off,auto]" can be used. If the parameter is specified the kernel and module code will be patched at runtime. Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch/s390/include/asm/nospec-branch.h')
1 files changed, 18 insertions, 0 deletions
diff --git a/arch/s390/include/asm/nospec-branch.h b/arch/s390/include/asm/nospec-branch.h
new file mode 100644
index 000000000000..7df48e5cf36f
--- /dev/null
+++ b/arch/s390/include/asm/nospec-branch.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_EXPOLINE_H
+#define _ASM_S390_EXPOLINE_H
+#ifndef __ASSEMBLY__
+#include <linux/types.h>
+extern int nospec_call_disable;
+extern int nospec_return_disable;
+void nospec_init_branches(void);
+void nospec_call_revert(s32 *start, s32 *end);
+void nospec_return_revert(s32 *start, s32 *end);
+#endif /* __ASSEMBLY__ */
+#endif /* _ASM_S390_EXPOLINE_H */

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