Messages in this thread | | | Subject | Re: [RFC v5 44/57] objtool: arm64: Implement functions to add switch tables alternatives | From | Raphael Gault <> | Date | Wed, 15 Jan 2020 16:37:19 +0000 |
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Hi Julien,
On 1/9/20 4:02 PM, Julien Thierry wrote: > This patch implements the functions required to identify and add as > alternatives all the possible destinations of the switch table. > This implementation relies on the new plugin introduced previously which > records information about the switch-table in a > .discard.switch_table_information section.
I think you forgot to update the name of the section with respect to what was done in the previous patch (.discard.switch_table_info instead of .discard.switch_table_information).
> > Signed-off-by: Raphael Gault <raphael.gault@arm.com> > [J.T.: Update arch implementation to new prototypes, > Update switch table information section name, > Do some clean up, > Use the offset sign information, > Use the newly added rela to find the corresponding jump instruction] > Signed-off-by: Julien Thierry <jthierry@redhat.com> > --- > tools/objtool/arch/arm64/arch_special.c | 251 +++++++++++++++++- > .../objtool/arch/arm64/include/arch_special.h | 2 + > tools/objtool/check.c | 4 +- > tools/objtool/check.h | 2 + > 4 files changed, 255 insertions(+), 4 deletions(-) > > diff --git a/tools/objtool/arch/arm64/arch_special.c b/tools/objtool/arch/arm64/arch_special.c > index 5239489c9c57..a15f6697dc74 100644 > --- a/tools/objtool/arch/arm64/arch_special.c > +++ b/tools/objtool/arch/arm64/arch_special.c > @@ -1,15 +1,262 @@ > // SPDX-License-Identifier: GPL-2.0-or-later > > +#include <stdlib.h> > +#include <string.h> > + > #include "../../special.h" > +#include "../../warn.h" > +#include "arch_special.h" > +#include "bit_operations.h" > +#include "insn_decode.h" > + > +/* > + * The arm64_switch_table_detection_plugin generate an array of elements > + * described by the following structure. > + * Each jump table found in the compilation unit is associated with one of > + * entries of the array. > + */ > +struct switch_table_info { > + u64 switch_table_ref; // Relocation target referencing the beginning of the jump table > + u64 dyn_jump_ref; // Relocation target referencing the set of instructions setting up the jump to the table > + u64 nb_entries; > + u64 offset_unsigned; > +} __attribute__((__packed__)); > + > +static bool insn_is_adr_pcrel(struct instruction *insn) > +{ > + u32 opcode = *(u32 *)(insn->sec->data->d_buf + insn->offset); > + > + return ((opcode >> 24) & 0x1f) == 0x10; > +} > + > +static s64 next_offset(void *table, u8 entry_size, bool is_signed) > +{ > + if (!is_signed) { > + switch (entry_size) { > + case 1: > + return *(u8 *)(table); > + case 2: > + return *(u16 *)(table); > + default: > + return *(u32 *)(table); > + } > + } else { > + switch (entry_size) { > + case 1: > + return *(s8 *)(table); > + case 2: > + return *(s16 *)(table); > + default: > + return *(s32 *)(table); > + } > + } > +} > + > +static u32 get_table_entry_size(u32 insn) > +{ > + unsigned char size = (insn >> 30) & ONES(2); > + > + switch (size) { > + case 0: > + return 1; > + case 1: > + return 2; > + default: > + return 4; > + } > +} > + > +static int add_possible_branch(struct objtool_file *file, > + struct instruction *insn, > + u32 base, s64 offset) > +{ > + struct instruction *dest_insn; > + struct alternative *alt; > + > + offset = base + 4 * offset; > + > + dest_insn = find_insn(file, insn->sec, offset); > + if (!dest_insn) > + return 0; > + > + alt = calloc(1, sizeof(*alt)); > + if (!alt) { > + WARN("allocation failure, can't add jump alternative"); > + return -1; > + } > + > + alt->insn = dest_insn; > + alt->skip_orig = true; > + list_add_tail(&alt->list, &insn->alts); > + return 0; > +} > + > +static struct switch_table_info *get_swt_info(struct section *swt_info_sec, > + struct instruction *insn) > +{ > + u64 *table_ref; > + > + if (!insn->jump_table) { > + WARN("no jump table available for %s+0x%lx", > + insn->sec->name, insn->offset); > + return NULL; > + } > + table_ref = (void *)(swt_info_sec->data->d_buf + > + insn->jump_table->offset); > + return container_of(table_ref, struct switch_table_info, > + switch_table_ref); > +} > + > +static int add_arm64_jump_table_dests(struct objtool_file *file, > + struct instruction *insn) > +{ > + struct switch_table_info *swt_info; > + struct section *objtool_data; > + struct section *rodata_sec; > + struct section *branch_sec; > + struct instruction *pre_jump_insn; > + u8 *switch_table; > + u32 entry_size; > + > + objtool_data = find_section_by_name(file->elf, > + ".discard.switch_table_info"); > + if (!objtool_data) > + return 0; > + > + /* > + * 1. Identify entry for the switch table > + * 2. Retrieve branch instruction > + * 3. Retrieve base offset > + * 3. For all entries in switch table: > + * 3.1. Compute new offset > + * 3.2. Create alternative instruction > + * 3.3. Add alt_instr to insn->alts list > + */ > + swt_info = get_swt_info(objtool_data, insn); > + > + /* retrieving pre jump instruction (ldr) */ > + branch_sec = insn->sec; > + pre_jump_insn = find_insn(file, branch_sec, > + insn->offset - 3 * sizeof(u32)); > + entry_size = get_table_entry_size(*(u32 *)(branch_sec->data->d_buf + > + pre_jump_insn->offset)); > + > + /* retrieving switch table content */ > + rodata_sec = find_section_by_name(file->elf, ".rodata"); > + switch_table = (u8 *)(rodata_sec->data->d_buf + > + insn->jump_table->addend); > + > + /* > + * iterating over the pre-jumps instruction in order to > + * retrieve switch base offset. > + */ > + while (pre_jump_insn && pre_jump_insn->offset <= insn->offset) { > + if (insn_is_adr_pcrel(pre_jump_insn)) { > + u64 base_offset; > + int i; > + > + base_offset = pre_jump_insn->offset + > + pre_jump_insn->immediate; > + > + /* > + * Once we have the switch table entry size > + * we add every possible destination using > + * alternatives of the original branch > + * instruction > + */ > + for (i = 0; i < swt_info->nb_entries; i++) { > + s64 table_offset = next_offset(switch_table, > + entry_size, > + !swt_info->offset_unsigned); > + > + if (add_possible_branch(file, insn, > + base_offset, > + table_offset)) { > + return -1; > + } > + switch_table += entry_size; > + } > + break; > + } > + pre_jump_insn = next_insn_same_sec(file, pre_jump_insn); > + } > + > + return 0; > +} > > int arch_add_jump_table_dests(struct objtool_file *file, > struct instruction *insn) > { > - return 0; > + return add_arm64_jump_table_dests(file, insn); > } > > +static struct rela *find_swt_info_jump_rela(struct section *swt_info_sec, > + u32 index) > +{ > + u32 rela_offset; > + > + rela_offset = index * sizeof(struct switch_table_info) + > + offsetof(struct switch_table_info, dyn_jump_ref); > + return find_rela_by_dest(swt_info_sec, rela_offset); > +} > + > +static struct rela *find_swt_info_table_rela(struct section *swt_info_sec, > + u32 index) > +{ > + u32 rela_offset; > + > + rela_offset = index * sizeof(struct switch_table_info) + > + offsetof(struct switch_table_info, switch_table_ref); > + return find_rela_by_dest(swt_info_sec, rela_offset); > +} > + > +/* > + * Aarch64 jump tables are just arrays of offsets (of varying size/signess) > + * representing the potential destination from a base address loaded by an adr > + * instruction. > + * > + * Aarch64 branches to jump tables are composed of multiple instructions: > + * > + * ldr<?> x_offset, [x_offsets_table, x_index, ...] > + * adr x_dest_base, <addr> > + * add x_dest, x_target_base, x_offset, ... > + * br x_dest > + * > + * The arm64_switch_table_detection_plugin will make the connection between > + * the instruction setting x_offsets_table (dyn_jump_ref) and the actual > + * table of offsets (switch_table_ref) > + */ > struct rela *arch_find_switch_table(struct objtool_file *file, > struct instruction *insn) > { > - return NULL; > + struct section *objtool_data; > + struct rela *res = NULL; > + u32 nb_swt_entries = 0; > + u32 i; > + > + objtool_data = find_section_by_name(file->elf, > + ".discard.switch_table_info"); > + if (objtool_data) > + nb_swt_entries = objtool_data->sh.sh_size / > + sizeof(struct switch_table_info); > + > + for (i = 0; i < nb_swt_entries; i++) { > + struct rela *info_rela; > + > + info_rela = find_swt_info_jump_rela(objtool_data, i); > + if (info_rela && info_rela->sym->sec == insn->sec && > + info_rela->addend == insn->offset) { > + if (res) { > + WARN_FUNC("duplicate objtool_data rela", > + info_rela->sec, info_rela->offset); > + continue; > + } > + res = find_swt_info_table_rela(objtool_data, i); > + if (!res) > + WARN_FUNC("missing relocation in objtool data", > + info_rela->sec, info_rela->offset); > + } > + } > + > + return res; > } > diff --git a/tools/objtool/arch/arm64/include/arch_special.h b/tools/objtool/arch/arm64/include/arch_special.h > index a82a9b3e51df..b96bcee308cf 100644 > --- a/tools/objtool/arch/arm64/include/arch_special.h > +++ b/tools/objtool/arch/arm64/include/arch_special.h > @@ -3,6 +3,8 @@ > #ifndef _ARM64_ARCH_SPECIAL_H > #define _ARM64_ARCH_SPECIAL_H > > +#include <linux/types.h> > + > #define EX_ENTRY_SIZE 8 > #define EX_ORIG_OFFSET 0 > #define EX_NEW_OFFSET 4 > diff --git a/tools/objtool/check.c b/tools/objtool/check.c > index e0c6bda261c8..80ea5bbd36ab 100644 > --- a/tools/objtool/check.c > +++ b/tools/objtool/check.c > @@ -33,8 +33,8 @@ struct instruction *find_insn(struct objtool_file *file, > return NULL; > } > > -static struct instruction *next_insn_same_sec(struct objtool_file *file, > - struct instruction *insn) > +struct instruction *next_insn_same_sec(struct objtool_file *file, > + struct instruction *insn) > { > struct instruction *next = list_next_entry(insn, list); > > diff --git a/tools/objtool/check.h b/tools/objtool/check.h > index 91adec42782c..15165d04d9cb 100644 > --- a/tools/objtool/check.h > +++ b/tools/objtool/check.h > @@ -66,6 +66,8 @@ int check(const char *objname, bool orc); > > struct instruction *find_insn(struct objtool_file *file, > struct section *sec, unsigned long offset); > +struct instruction *next_insn_same_sec(struct objtool_file *file, > + struct instruction *insn); > > #define for_each_insn(file, insn) \ > list_for_each_entry(insn, &file->insn_list, list) >
Cheers,
-- Raphaël Gault
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