From d6e2cc56477538255160ed02fdb11b0da60356cc Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Tue, 19 Oct 2021 17:02:16 +0100 Subject: [PATCH] arm64: extable: add `type` and `data` fields Subsequent patches will add specialized handlers for fixups, in addition to the simple PC fixup and BPF handlers we have today. In preparation, this patch adds a new `type` field to struct exception_table_entry, and uses this to distinguish the fixup and BPF cases. A `data` field is also added so that subsequent patches can associate data specific to each exception site (e.g. register numbers). Handlers are named ex_handler_*() for consistency, following the exmaple of x86. At the same time, get_ex_fixup() is split out into a helper so that it can be used by other ex_handler_*() functions ins subsequent patches. This patch will increase the size of the exception tables, which will be remedied by subsequent patches removing redundant fixup code. There should be no functional change as a result of this patch. Since each entry is now 12 bytes in size, we must reduce the alignment of each entry from `.align 3` (i.e. 8 bytes) to `.align 2` (i.e. 4 bytes), which is the natrual alignment of the `insn` and `fixup` fields. The current 8-byte alignment is a holdover from when the `insn` and `fixup` fields was 8 bytes, and while not harmful has not been necessary since commit: 6c94f27ac847ff8e ("arm64: switch to relative exception tables") Similarly, RO_EXCEPTION_TABLE_ALIGN is dropped to 4 bytes. Concurrently with this patch, x86's exception table entry format is being updated (similarly to a 12-byte format, with 32-bytes of absolute data). Once both have been merged it should be possible to unify the sorttable logic for the two. Signed-off-by: Mark Rutland Reviewed-by: Ard Biesheuvel Cc: Alexei Starovoitov Cc: Andrii Nakryiko Cc: Catalin Marinas Cc: Daniel Borkmann Cc: James Morse Cc: Jean-Philippe Brucker Cc: Robin Murphy Cc: Will Deacon Link: https://lore.kernel.org/r/20211019160219.5202-11-mark.rutland@arm.com Signed-off-by: Will Deacon --- arch/arm64/include/asm/asm-extable.h | 32 ++++++++++++++++++++------------ arch/arm64/include/asm/extable.h | 19 +++++++++++++++---- arch/arm64/kernel/vmlinux.lds.S | 2 +- arch/arm64/mm/extable.c | 29 +++++++++++++++++++++++++---- arch/arm64/net/bpf_jit_comp.c | 7 +++++-- scripts/sorttable.c | 30 ++++++++++++++++++++++++++++++ 6 files changed, 96 insertions(+), 23 deletions(-) diff --git a/arch/arm64/include/asm/asm-extable.h b/arch/arm64/include/asm/asm-extable.h index 986b4c0..5ee748e 100644 --- a/arch/arm64/include/asm/asm-extable.h +++ b/arch/arm64/include/asm/asm-extable.h @@ -2,13 +2,19 @@ #ifndef __ASM_ASM_EXTABLE_H #define __ASM_ASM_EXTABLE_H +#define EX_TYPE_NONE 0 +#define EX_TYPE_FIXUP 1 +#define EX_TYPE_BPF 2 + #ifdef __ASSEMBLY__ -#define __ASM_EXTABLE_RAW(insn, fixup) \ - .pushsection __ex_table, "a"; \ - .align 3; \ - .long ((insn) - .); \ - .long ((fixup) - .); \ +#define __ASM_EXTABLE_RAW(insn, fixup, type, data) \ + .pushsection __ex_table, "a"; \ + .align 2; \ + .long ((insn) - .); \ + .long ((fixup) - .); \ + .short (type); \ + .short (data); \ .popsection; /* @@ -16,7 +22,7 @@ * when an unhandled fault is taken. */ .macro _asm_extable, insn, fixup - __ASM_EXTABLE_RAW(\insn, \fixup) + __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_FIXUP, 0) .endm /* @@ -33,15 +39,17 @@ #include -#define __ASM_EXTABLE_RAW(insn, fixup) \ - ".pushsection __ex_table, \"a\"\n" \ - ".align 3\n" \ - ".long ((" insn ") - .)\n" \ - ".long ((" fixup ") - .)\n" \ +#define __ASM_EXTABLE_RAW(insn, fixup, type, data) \ + ".pushsection __ex_table, \"a\"\n" \ + ".align 2\n" \ + ".long ((" insn ") - .)\n" \ + ".long ((" fixup ") - .)\n" \ + ".short (" type ")\n" \ + ".short (" data ")\n" \ ".popsection\n" #define _ASM_EXTABLE(insn, fixup) \ - __ASM_EXTABLE_RAW(#insn, #fixup) + __ASM_EXTABLE_RAW(#insn, #fixup, __stringify(EX_TYPE_FIXUP), "0") #endif /* __ASSEMBLY__ */ diff --git a/arch/arm64/include/asm/extable.h b/arch/arm64/include/asm/extable.h index 1859b9f..8b300dd 100644 --- a/arch/arm64/include/asm/extable.h +++ b/arch/arm64/include/asm/extable.h @@ -18,10 +18,21 @@ struct exception_table_entry { int insn, fixup; + short type, data; }; #define ARCH_HAS_RELATIVE_EXTABLE +#define swap_ex_entry_fixup(a, b, tmp, delta) \ +do { \ + (a)->fixup = (b)->fixup + (delta); \ + (b)->fixup = (tmp).fixup - (delta); \ + (a)->type = (b)->type; \ + (b)->type = (tmp).type; \ + (a)->data = (b)->data; \ + (b)->data = (tmp).data; \ +} while (0) + static inline bool in_bpf_jit(struct pt_regs *regs) { if (!IS_ENABLED(CONFIG_BPF_JIT)) @@ -32,12 +43,12 @@ static inline bool in_bpf_jit(struct pt_regs *regs) } #ifdef CONFIG_BPF_JIT -bool arm64_bpf_fixup_exception(const struct exception_table_entry *ex, - struct pt_regs *regs); +bool ex_handler_bpf(const struct exception_table_entry *ex, + struct pt_regs *regs); #else /* !CONFIG_BPF_JIT */ static inline -bool arm64_bpf_fixup_exception(const struct exception_table_entry *ex, - struct pt_regs *regs) +bool ex_handler_bpf(const struct exception_table_entry *ex, + struct pt_regs *regs) { return false; } diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index f6b1a88..fa8a8e8 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -57,7 +57,7 @@ #define SBSS_ALIGN 0 #endif -#define RO_EXCEPTION_TABLE_ALIGN 8 +#define RO_EXCEPTION_TABLE_ALIGN 4 #define RUNTIME_DISCARD_EXIT #include diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c index dba3d59..c2951b9 100644 --- a/arch/arm64/mm/extable.c +++ b/arch/arm64/mm/extable.c @@ -6,6 +6,24 @@ #include #include +#include + +typedef bool (*ex_handler_t)(const struct exception_table_entry *, + struct pt_regs *); + +static inline unsigned long +get_ex_fixup(const struct exception_table_entry *ex) +{ + return ((unsigned long)&ex->fixup + ex->fixup); +} + +static bool ex_handler_fixup(const struct exception_table_entry *ex, + struct pt_regs *regs) +{ + regs->pc = get_ex_fixup(ex); + return true; +} + bool fixup_exception(struct pt_regs *regs) { const struct exception_table_entry *ex; @@ -14,9 +32,12 @@ bool fixup_exception(struct pt_regs *regs) if (!ex) return false; - if (in_bpf_jit(regs)) - return arm64_bpf_fixup_exception(ex, regs); + switch (ex->type) { + case EX_TYPE_FIXUP: + return ex_handler_fixup(ex, regs); + case EX_TYPE_BPF: + return ex_handler_bpf(ex, regs); + } - regs->pc = (unsigned long)&ex->fixup + ex->fixup; - return true; + BUG(); } diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c index 956c841..7df7345 100644 --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -13,6 +13,7 @@ #include #include +#include #include #include #include @@ -358,8 +359,8 @@ static void build_epilogue(struct jit_ctx *ctx) #define BPF_FIXUP_OFFSET_MASK GENMASK(26, 0) #define BPF_FIXUP_REG_MASK GENMASK(31, 27) -bool arm64_bpf_fixup_exception(const struct exception_table_entry *ex, - struct pt_regs *regs) +bool ex_handler_bpf(const struct exception_table_entry *ex, + struct pt_regs *regs) { off_t offset = FIELD_GET(BPF_FIXUP_OFFSET_MASK, ex->fixup); int dst_reg = FIELD_GET(BPF_FIXUP_REG_MASK, ex->fixup); @@ -412,6 +413,8 @@ static int add_exception_handler(const struct bpf_insn *insn, ex->fixup = FIELD_PREP(BPF_FIXUP_OFFSET_MASK, offset) | FIELD_PREP(BPF_FIXUP_REG_MASK, dst_reg); + ex->type = EX_TYPE_BPF; + ctx->exentry_idx++; return 0; } diff --git a/scripts/sorttable.c b/scripts/sorttable.c index 6ee4fa8..ee95bb4 100644 --- a/scripts/sorttable.c +++ b/scripts/sorttable.c @@ -231,6 +231,34 @@ static void sort_relative_table(char *extab_image, int image_size) } } +static void arm64_sort_relative_table(char *extab_image, int image_size) +{ + int i = 0; + + while (i < image_size) { + uint32_t *loc = (uint32_t *)(extab_image + i); + + w(r(loc) + i, loc); + w(r(loc + 1) + i + 4, loc + 1); + /* Don't touch the fixup type or data */ + + i += sizeof(uint32_t) * 3; + } + + qsort(extab_image, image_size / 12, 12, compare_relative_table); + + i = 0; + while (i < image_size) { + uint32_t *loc = (uint32_t *)(extab_image + i); + + w(r(loc) - i, loc); + w(r(loc + 1) - (i + 4), loc + 1); + /* Don't touch the fixup type or data */ + + i += sizeof(uint32_t) * 3; + } +} + static void x86_sort_relative_table(char *extab_image, int image_size) { int i = 0; @@ -343,6 +371,8 @@ static int do_file(char const *const fname, void *addr) custom_sort = s390_sort_relative_table; break; case EM_AARCH64: + custom_sort = arm64_sort_relative_table; + break; case EM_PARISC: case EM_PPC: case EM_PPC64: -- 2.7.4