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authorMartin Schwidefsky <schwidefsky@de.ibm.com>2018-04-25 18:35:26 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-05-30 07:49:17 +0200
commitb4ab3567f276ef0603ddd205d4eaa39b417808be (patch)
treeefa269c77f638f6d43e81fc5b9f34ef4c6df529a
parente612f1ce0509ea7a53c3915ea6f7855ee5a0efe0 (diff)
s390/ftrace: use expoline for indirect branches
commit 23a4d7fd34856da8218c4cfc23dba7a6ec0a423a upstream. The return from the ftrace_stub, _mcount, ftrace_caller and return_to_handler functions is done with "br %r14" and "br %r1". These are indirect branches as well and need to use execute trampolines for CONFIG_EXPOLINE=y. The ftrace_caller function is a special case as it returns to the start of a function and may only use %r0 and %r1. For a pre z10 machine the standard execute trampoline uses a LARL + EX to do this, but this requires *two* registers in the range %r1..%r15. To get around this the 'br %r1' located in the lowcore is used, then the EX instruction does not need an address register. But the lowcore trick may only be used for pre z14 machines, with noexec=on the mapping for the first page may not contain instructions. The solution for that is an ALTERNATIVE in the expoline THUNK generated by 'GEN_BR_THUNK %r1' to switch to EXRL, this relies on the fact that a machine that supports noexec=on has EXRL as well. Cc: stable@vger.kernel.org # 4.16 Fixes: f19fbd5ed6 ("s390: introduce execute-trampolines for branches") Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--arch/s390/include/asm/nospec-insn.h13
-rw-r--r--arch/s390/kernel/asm-offsets.c1
-rw-r--r--arch/s390/kernel/mcount.S14
3 files changed, 23 insertions, 5 deletions
diff --git a/arch/s390/include/asm/nospec-insn.h b/arch/s390/include/asm/nospec-insn.h
index 087fc9b972c5..9a56e738d645 100644
--- a/arch/s390/include/asm/nospec-insn.h
+++ b/arch/s390/include/asm/nospec-insn.h
@@ -2,10 +2,15 @@
#ifndef _ASM_S390_NOSPEC_ASM_H
#define _ASM_S390_NOSPEC_ASM_H
+#include <asm/alternative-asm.h>
+#include <asm/asm-offsets.h>
+
#ifdef __ASSEMBLY__
#ifdef CONFIG_EXPOLINE
+_LC_BR_R1 = __LC_BR_R1
+
/*
* The expoline macros are used to create thunks in the same format
* as gcc generates them. The 'comdat' section flag makes sure that
@@ -101,13 +106,21 @@
.endm
.macro __THUNK_EX_BR reg,ruse
+ # Be very careful when adding instructions to this macro!
+ # The ALTERNATIVE replacement code has a .+10 which targets
+ # the "br \reg" after the code has been patched.
#ifdef CONFIG_HAVE_MARCH_Z10_FEATURES
exrl 0,555f
j .
#else
+ .ifc \reg,%r1
+ ALTERNATIVE "ex %r0,_LC_BR_R1", ".insn ril,0xc60000000000,0,.+10", 35
+ j .
+ .else
larl \ruse,555f
ex 0,0(\ruse)
j .
+ .endif
#endif
555: br \reg
.endm
diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index dc6c9c604543..39572281e213 100644
--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -170,6 +170,7 @@ int main(void)
OFFSET(__LC_MACHINE_FLAGS, _lowcore, machine_flags);
OFFSET(__LC_GMAP, _lowcore, gmap);
OFFSET(__LC_PASTE, _lowcore, paste);
+ OFFSET(__LC_BR_R1, _lowcore, br_r1_trampoline);
/* software defined ABI-relevant lowcore locations 0xe00 - 0xe20 */
OFFSET(__LC_DUMP_REIPL, _lowcore, ipib);
/* hardware defined lowcore locations 0x1000 - 0x18ff */
diff --git a/arch/s390/kernel/mcount.S b/arch/s390/kernel/mcount.S
index e499370fbccb..6c1c7d399bf9 100644
--- a/arch/s390/kernel/mcount.S
+++ b/arch/s390/kernel/mcount.S
@@ -8,12 +8,16 @@
#include <linux/linkage.h>
#include <asm/asm-offsets.h>
#include <asm/ftrace.h>
+#include <asm/nospec-insn.h>
#include <asm/ptrace.h>
+ GEN_BR_THUNK %r1
+ GEN_BR_THUNK %r14
+
.section .kprobes.text, "ax"
ENTRY(ftrace_stub)
- br %r14
+ BR_EX %r14
#define STACK_FRAME_SIZE (STACK_FRAME_OVERHEAD + __PT_SIZE)
#define STACK_PTREGS (STACK_FRAME_OVERHEAD)
@@ -21,7 +25,7 @@ ENTRY(ftrace_stub)
#define STACK_PTREGS_PSW (STACK_PTREGS + __PT_PSW)
ENTRY(_mcount)
- br %r14
+ BR_EX %r14
ENTRY(ftrace_caller)
.globl ftrace_regs_caller
@@ -49,7 +53,7 @@ ENTRY(ftrace_caller)
#endif
lgr %r3,%r14
la %r5,STACK_PTREGS(%r15)
- basr %r14,%r1
+ BASR_EX %r14,%r1
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
# The j instruction gets runtime patched to a nop instruction.
# See ftrace_enable_ftrace_graph_caller.
@@ -64,7 +68,7 @@ ftrace_graph_caller_end:
#endif
lg %r1,(STACK_PTREGS_PSW+8)(%r15)
lmg %r2,%r15,(STACK_PTREGS_GPRS+2*8)(%r15)
- br %r1
+ BR_EX %r1
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
@@ -77,6 +81,6 @@ ENTRY(return_to_handler)
aghi %r15,STACK_FRAME_OVERHEAD
lgr %r14,%r2
lmg %r2,%r5,32(%r15)
- br %r14
+ BR_EX %r14
#endif