diff options
| 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/include/asm | |
| 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/include/asm')
| -rw-r--r-- | arch/s390/include/asm/nospec-insn.h | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/arch/s390/include/asm/nospec-insn.h b/arch/s390/include/asm/nospec-insn.h index 440689cbcf51..7d7640e1cf90 100644 --- a/arch/s390/include/asm/nospec-insn.h +++ b/arch/s390/include/asm/nospec-insn.h @@ -2,12 +2,16 @@ #ifndef _ASM_S390_NOSPEC_ASM_H #define _ASM_S390_NOSPEC_ASM_H +#include <asm/alternative-asm.h> +#include <asm/asm-offsets.h> #include <asm/dwarf.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 @@ -78,13 +82,21 @@ .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 |