diff options
Diffstat (limited to 'arch/s390/kernel/nospec-branch.c')
-rw-r--r-- | arch/s390/kernel/nospec-branch.c | 100 |
1 files changed, 100 insertions, 0 deletions
diff --git a/arch/s390/kernel/nospec-branch.c b/arch/s390/kernel/nospec-branch.c new file mode 100644 index 0000000..69d7fcf --- /dev/null +++ b/arch/s390/kernel/nospec-branch.c @@ -0,0 +1,100 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <linux/module.h> +#include <asm/nospec-branch.h> + +int nospec_call_disable = IS_ENABLED(EXPOLINE_OFF); +int nospec_return_disable = !IS_ENABLED(EXPOLINE_FULL); + +static int __init nospectre_v2_setup_early(char *str) +{ + nospec_call_disable = 1; + nospec_return_disable = 1; + return 0; +} +early_param("nospectre_v2", nospectre_v2_setup_early); + +static int __init spectre_v2_setup_early(char *str) +{ + if (str && !strncmp(str, "on", 2)) { + nospec_call_disable = 0; + nospec_return_disable = 0; + } + if (str && !strncmp(str, "off", 3)) { + nospec_call_disable = 1; + nospec_return_disable = 1; + } + if (str && !strncmp(str, "auto", 4)) { + nospec_call_disable = 0; + nospec_return_disable = 1; + } + return 0; +} +early_param("spectre_v2", spectre_v2_setup_early); + +static void __init_or_module __nospec_revert(s32 *start, s32 *end) +{ + enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type; + u8 *instr, *thunk, *br; + u8 insnbuf[6]; + s32 *epo; + + /* Second part of the instruction replace is always a nop */ + memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x00, 0x00 }, 4); + for (epo = start; epo < end; epo++) { + instr = (u8 *) epo + *epo; + if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04) + type = BRCL_EXPOLINE; /* brcl instruction */ + else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05) + type = BRASL_EXPOLINE; /* brasl instruction */ + else + continue; + thunk = instr + (*(int *)(instr + 2)) * 2; + if (thunk[0] == 0xc6 && thunk[1] == 0x00) + /* exrl %r0,<target-br> */ + br = thunk + (*(int *)(thunk + 2)) * 2; + else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 && + thunk[6] == 0x44 && thunk[7] == 0x00 && + (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 && + (thunk[1] & 0xf0) == (thunk[8] & 0xf0)) + /* larl %rx,<target br> + ex %r0,0(%rx) */ + br = thunk + (*(int *)(thunk + 2)) * 2; + else + continue; + if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0) + continue; + switch (type) { + case BRCL_EXPOLINE: + /* brcl to thunk, replace with br + nop */ + insnbuf[0] = br[0]; + insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); + break; + case BRASL_EXPOLINE: + /* brasl to thunk, replace with basr + nop */ + insnbuf[0] = 0x0d; + insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); + break; + } + + s390_kernel_write(instr, insnbuf, 6); + } +} + +void __init_or_module nospec_call_revert(s32 *start, s32 *end) +{ + if (nospec_call_disable) + __nospec_revert(start, end); +} + +void __init_or_module nospec_return_revert(s32 *start, s32 *end) +{ + if (nospec_return_disable) + __nospec_revert(start, end); +} + +extern s32 __nospec_call_start[], __nospec_call_end[]; +extern s32 __nospec_return_start[], __nospec_return_end[]; +void __init nospec_init_branches(void) +{ + nospec_call_revert(__nospec_call_start, __nospec_call_end); + nospec_return_revert(__nospec_return_start, __nospec_return_end); +} |