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| author | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2018-04-25 18:35:26 +0200 |
|---|---|---|
| committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2018-05-07 21:12:38 +0200 |
| commit | 23a4d7fd34856da8218c4cfc23dba7a6ec0a423a (patch) | |
| tree | f6bf7c9d6e0f61af64bba6877562e63793b8e4c1 /arch/s390/kernel/mcount.S | |
| parent | 97489e0663fa700d6e7febddc43b58df98d7bcda (diff) | |
s390/ftrace: use expoline for indirect branches
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>
Diffstat (limited to 'arch/s390/kernel/mcount.S')
| -rw-r--r-- | arch/s390/kernel/mcount.S | 14 |
1 files changed, 9 insertions, 5 deletions
diff --git a/arch/s390/kernel/mcount.S b/arch/s390/kernel/mcount.S index 82df7d80fab2..27110f3294ed 100644 --- a/arch/s390/kernel/mcount.S +++ b/arch/s390/kernel/mcount.S @@ -9,13 +9,17 @@ #include <linux/linkage.h> #include <asm/asm-offsets.h> #include <asm/ftrace.h> +#include <asm/nospec-insn.h> #include <asm/ptrace.h> #include <asm/export.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) @@ -23,7 +27,7 @@ ENTRY(ftrace_stub) #define STACK_PTREGS_PSW (STACK_PTREGS + __PT_PSW) ENTRY(_mcount) - br %r14 + BR_EX %r14 EXPORT_SYMBOL(_mcount) @@ -53,7 +57,7 @@ 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. @@ -68,7 +72,7 @@ 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 @@ -81,6 +85,6 @@ ENTRY(return_to_handler) aghi %r15,STACK_FRAME_OVERHEAD lgr %r14,%r2 lmg %r2,%r5,32(%r15) - br %r14 + BR_EX %r14 #endif |