MIPS: Check Loongson3 LL/SC errata workaround correctness
When Loongson3 LL/SC errata workarounds are enabled (ie.
CONFIG_CPU_LOONGSON3_WORKAROUNDS=y) run a tool to scan through the
compiled kernel & ensure that the workaround is applied correctly. That
is, ensure that:
- Every LL or LLD instruction is preceded by a sync instruction.
- Any branches from within an LL/SC loop to outside of that loop
target a sync instruction.
Reasoning for these conditions can be found by reading the comment above
the definition of __SYNC_loongson3_war in arch/mips/include/asm/sync.h.
This tool will help ensure that we don't inadvertently introduce code
paths that miss the required workarounds.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Series-changes: 2
- Only try to build loongson3-llsc-check from arch/mips/Makefile when
CONFIG_CPU_LOONGSON3_WORKAROUNDS is enabled.
Series-version: 3
Series-to: linux-mips@vger.kernel.org
Series-cc: linux-kernel@vger.kernel.org
Series-cc: Huacai Chen <chenhc@lemote.com>
Series-cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cover-letter:
MIPS: barriers & atomics cleanups
This series consists of a bunch of cleanups to the way we handle memory
barriers (though no changes to the sync instructions we use to implement
them) & atomic memory accesses. One major goal was to ensure the
Loongson3 LL/SC errata workarounds are applied in a safe manner from
within inline-asm & that we can automatically verify the resulting
kernel binary looks reasonable. Many patches are cleanups found along
the way.
Applies atop v5.4-rc1.
Changes in v2:
- Keep our fls/ffs implementations. Turns out GCC's builtins call
intrinsics in some configurations, and if we'd need to go implement
those then using the generic fls/ffs doesn't seem like such a win.
- De-string __WEAK_LLSC_MB to allow use with __SYNC_ELSE().
- Only try to build the loongson3-llsc-check tool from
arch/mips/Makefile when CONFIG_CPU_LOONGSON3_WORKAROUNDS is enabled.
Changes in v3:
- Restore "\n" after __WEAK_LLSC_MB use in asm/futex.h.
END
diff --git a/arch/mips/Makefile b/arch/mips/Makefile
index cdc09b7..0a5eab62 100644
--- a/arch/mips/Makefile
+++ b/arch/mips/Makefile
@@ -14,6 +14,9 @@
archscripts: scripts_basic
$(Q)$(MAKE) $(build)=arch/mips/tools elf-entry
+ifeq ($(CONFIG_CPU_LOONGSON3_WORKAROUNDS),y)
+ $(Q)$(MAKE) $(build)=arch/mips/tools loongson3-llsc-check
+endif
$(Q)$(MAKE) $(build)=arch/mips/boot/tools relocs
KBUILD_DEFCONFIG := 32r2el_defconfig
diff --git a/arch/mips/Makefile.postlink b/arch/mips/Makefile.postlink
index 4eea418..f03fdc9 100644
--- a/arch/mips/Makefile.postlink
+++ b/arch/mips/Makefile.postlink
@@ -3,7 +3,8 @@
# Post-link MIPS pass
# ===========================================================================
#
-# 1. Insert relocations into vmlinux
+# 1. Check that Loongson3 LL/SC workarounds are applied correctly
+# 2. Insert relocations into vmlinux
PHONY := __archpost
__archpost:
@@ -11,6 +12,10 @@
-include include/config/auto.conf
include scripts/Kbuild.include
+CMD_LS3_LLSC = arch/mips/tools/loongson3-llsc-check
+quiet_cmd_ls3_llsc = LLSCCHK $@
+ cmd_ls3_llsc = $(CMD_LS3_LLSC) $@
+
CMD_RELOCS = arch/mips/boot/tools/relocs
quiet_cmd_relocs = RELOCS $@
cmd_relocs = $(CMD_RELOCS) $@
@@ -19,6 +24,9 @@
vmlinux: FORCE
@true
+ifeq ($(CONFIG_CPU_LOONGSON3_WORKAROUNDS),y)
+ $(call if_changed,ls3_llsc)
+endif
ifeq ($(CONFIG_RELOCATABLE),y)
$(call if_changed,relocs)
endif
diff --git a/arch/mips/tools/.gitignore b/arch/mips/tools/.gitignore
index 56d34cc..b020945 100644
--- a/arch/mips/tools/.gitignore
+++ b/arch/mips/tools/.gitignore
@@ -1 +1,2 @@
elf-entry
+loongson3-llsc-check
diff --git a/arch/mips/tools/Makefile b/arch/mips/tools/Makefile
index 3baee4b..aaef688 100644
--- a/arch/mips/tools/Makefile
+++ b/arch/mips/tools/Makefile
@@ -3,3 +3,8 @@
PHONY += elf-entry
elf-entry: $(obj)/elf-entry
@:
+
+hostprogs-$(CONFIG_CPU_LOONGSON3_WORKAROUNDS) += loongson3-llsc-check
+PHONY += loongson3-llsc-check
+loongson3-llsc-check: $(obj)/loongson3-llsc-check
+ @:
diff --git a/arch/mips/tools/loongson3-llsc-check.c b/arch/mips/tools/loongson3-llsc-check.c
new file mode 100644
index 0000000..0ebddd0
--- /dev/null
+++ b/arch/mips/tools/loongson3-llsc-check.c
@@ -0,0 +1,307 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <byteswap.h>
+#include <elf.h>
+#include <endian.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <inttypes.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#ifdef be32toh
+/* If libc provides le{16,32,64}toh() then we'll use them */
+#elif BYTE_ORDER == LITTLE_ENDIAN
+# define le16toh(x) (x)
+# define le32toh(x) (x)
+# define le64toh(x) (x)
+#elif BYTE_ORDER == BIG_ENDIAN
+# define le16toh(x) bswap_16(x)
+# define le32toh(x) bswap_32(x)
+# define le64toh(x) bswap_64(x)
+#endif
+
+/* MIPS opcodes, in bits 31:26 of an instruction */
+#define OP_SPECIAL 0x00
+#define OP_REGIMM 0x01
+#define OP_BEQ 0x04
+#define OP_BNE 0x05
+#define OP_BLEZ 0x06
+#define OP_BGTZ 0x07
+#define OP_BEQL 0x14
+#define OP_BNEL 0x15
+#define OP_BLEZL 0x16
+#define OP_BGTZL 0x17
+#define OP_LL 0x30
+#define OP_LLD 0x34
+#define OP_SC 0x38
+#define OP_SCD 0x3c
+
+/* Bits 20:16 of OP_REGIMM instructions */
+#define REGIMM_BLTZ 0x00
+#define REGIMM_BGEZ 0x01
+#define REGIMM_BLTZL 0x02
+#define REGIMM_BGEZL 0x03
+#define REGIMM_BLTZAL 0x10
+#define REGIMM_BGEZAL 0x11
+#define REGIMM_BLTZALL 0x12
+#define REGIMM_BGEZALL 0x13
+
+/* Bits 5:0 of OP_SPECIAL instructions */
+#define SPECIAL_SYNC 0x0f
+
+static void usage(FILE *f)
+{
+ fprintf(f, "Usage: loongson3-llsc-check /path/to/vmlinux\n");
+}
+
+static int se16(uint16_t x)
+{
+ return (int16_t)x;
+}
+
+static bool is_ll(uint32_t insn)
+{
+ switch (insn >> 26) {
+ case OP_LL:
+ case OP_LLD:
+ return true;
+
+ default:
+ return false;
+ }
+}
+
+static bool is_sc(uint32_t insn)
+{
+ switch (insn >> 26) {
+ case OP_SC:
+ case OP_SCD:
+ return true;
+
+ default:
+ return false;
+ }
+}
+
+static bool is_sync(uint32_t insn)
+{
+ /* Bits 31:11 should all be zeroes */
+ if (insn >> 11)
+ return false;
+
+ /* Bits 5:0 specify the SYNC special encoding */
+ if ((insn & 0x3f) != SPECIAL_SYNC)
+ return false;
+
+ return true;
+}
+
+static bool is_branch(uint32_t insn, int *off)
+{
+ switch (insn >> 26) {
+ case OP_BEQ:
+ case OP_BEQL:
+ case OP_BNE:
+ case OP_BNEL:
+ case OP_BGTZ:
+ case OP_BGTZL:
+ case OP_BLEZ:
+ case OP_BLEZL:
+ *off = se16(insn) + 1;
+ return true;
+
+ case OP_REGIMM:
+ switch ((insn >> 16) & 0x1f) {
+ case REGIMM_BGEZ:
+ case REGIMM_BGEZL:
+ case REGIMM_BGEZAL:
+ case REGIMM_BGEZALL:
+ case REGIMM_BLTZ:
+ case REGIMM_BLTZL:
+ case REGIMM_BLTZAL:
+ case REGIMM_BLTZALL:
+ *off = se16(insn) + 1;
+ return true;
+
+ default:
+ return false;
+ }
+
+ default:
+ return false;
+ }
+}
+
+static int check_ll(uint64_t pc, uint32_t *code, size_t sz)
+{
+ ssize_t i, max, sc_pos;
+ int off;
+
+ /*
+ * Every LL must be preceded by a sync instruction in order to ensure
+ * that instruction reordering doesn't allow a prior memory access to
+ * execute after the LL & cause erroneous results.
+ */
+ if (!is_sync(le32toh(code[-1]))) {
+ fprintf(stderr, "%" PRIx64 ": LL not preceded by sync\n", pc);
+ return -EINVAL;
+ }
+
+ /* Find the matching SC instruction */
+ max = sz / 4;
+ for (sc_pos = 0; sc_pos < max; sc_pos++) {
+ if (is_sc(le32toh(code[sc_pos])))
+ break;
+ }
+ if (sc_pos >= max) {
+ fprintf(stderr, "%" PRIx64 ": LL has no matching SC\n", pc);
+ return -EINVAL;
+ }
+
+ /*
+ * Check branches within the LL/SC loop target sync instructions,
+ * ensuring that speculative execution can't generate memory accesses
+ * due to instructions outside of the loop.
+ */
+ for (i = 0; i < sc_pos; i++) {
+ if (!is_branch(le32toh(code[i]), &off))
+ continue;
+
+ /*
+ * If the branch target is within the LL/SC loop then we don't
+ * need to worry about it.
+ */
+ if ((off >= -i) && (off <= sc_pos))
+ continue;
+
+ /* If the branch targets a sync instruction we're all good... */
+ if (is_sync(le32toh(code[i + off])))
+ continue;
+
+ /* ...but if not, we have a problem */
+ fprintf(stderr, "%" PRIx64 ": Branch target not a sync\n",
+ pc + (i * 4));
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+static int check_code(uint64_t pc, uint32_t *code, size_t sz)
+{
+ int err = 0;
+
+ if (sz % 4) {
+ fprintf(stderr, "%" PRIx64 ": Section size not a multiple of 4\n",
+ pc);
+ err = -EINVAL;
+ sz -= (sz % 4);
+ }
+
+ if (is_ll(le32toh(code[0]))) {
+ fprintf(stderr, "%" PRIx64 ": First instruction in section is an LL\n",
+ pc);
+ err = -EINVAL;
+ }
+
+#define advance() ( \
+ code++, \
+ pc += 4, \
+ sz -= 4 \
+)
+
+ /*
+ * Skip the first instructionm allowing check_ll to look backwards
+ * unconditionally.
+ */
+ advance();
+
+ /* Now scan through the code looking for LL instructions */
+ for (; sz; advance()) {
+ if (is_ll(le32toh(code[0])))
+ err |= check_ll(pc, code, sz);
+ }
+
+ return err;
+}
+
+int main(int argc, char *argv[])
+{
+ int vmlinux_fd, status, err, i;
+ const char *vmlinux_path;
+ struct stat st;
+ Elf64_Ehdr *eh;
+ Elf64_Shdr *sh;
+ void *vmlinux;
+
+ status = EXIT_FAILURE;
+
+ if (argc < 2) {
+ usage(stderr);
+ goto out_ret;
+ }
+
+ vmlinux_path = argv[1];
+ vmlinux_fd = open(vmlinux_path, O_RDONLY);
+ if (vmlinux_fd == -1) {
+ perror("Unable to open vmlinux");
+ goto out_ret;
+ }
+
+ err = fstat(vmlinux_fd, &st);
+ if (err) {
+ perror("Unable to stat vmlinux");
+ goto out_close;
+ }
+
+ vmlinux = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, vmlinux_fd, 0);
+ if (vmlinux == MAP_FAILED) {
+ perror("Unable to mmap vmlinux");
+ goto out_close;
+ }
+
+ eh = vmlinux;
+ if (memcmp(eh->e_ident, ELFMAG, SELFMAG)) {
+ fprintf(stderr, "vmlinux is not an ELF?\n");
+ goto out_munmap;
+ }
+
+ if (eh->e_ident[EI_CLASS] != ELFCLASS64) {
+ fprintf(stderr, "vmlinux is not 64b?\n");
+ goto out_munmap;
+ }
+
+ if (eh->e_ident[EI_DATA] != ELFDATA2LSB) {
+ fprintf(stderr, "vmlinux is not little endian?\n");
+ goto out_munmap;
+ }
+
+ for (i = 0; i < le16toh(eh->e_shnum); i++) {
+ sh = vmlinux + le64toh(eh->e_shoff) + (i * le16toh(eh->e_shentsize));
+
+ if (sh->sh_type != SHT_PROGBITS)
+ continue;
+ if (!(sh->sh_flags & SHF_EXECINSTR))
+ continue;
+
+ err = check_code(le64toh(sh->sh_addr),
+ vmlinux + le64toh(sh->sh_offset),
+ le64toh(sh->sh_size));
+ if (err)
+ goto out_munmap;
+ }
+
+ status = EXIT_SUCCESS;
+out_munmap:
+ munmap(vmlinux, st.st_size);
+out_close:
+ close(vmlinux_fd);
+out_ret:
+ return status;
+}
