From 8c078abdc23238c2193136bf0edbf1d910615679 Mon Sep 17 00:00:00 2001 From: Indu Bhagat Date: Thu, 15 Dec 2022 13:12:01 -0800 Subject: [PATCH] libsframe asan: avoid generating misaligned loads There are two places where unaligned loads were seen on aarch64: - #1. access to the SFrame FRE stack offsets in the in-memory representation/abstraction provided by libsframe. - #2. access to the SFrame FRE start address in the on-disk representation of the frame row entry. For #1, we can fix this by reordering the struct members of sframe_frame_row_entry in libsframe/sframe-api.h. For #2, we need to default to using memcpy instead, and copy out the bytes to a location for output. SFrame format is an unaligned on-disk format. As such, there are other blobs of memory in the on-disk SFrame FRE that are on not on their natural boundaries. But that does not pose further problems yet, because the users are provided access to the on-disk SFrame FRE data via libsframe's sframe_frame_row_entry, the latter has its' struct members aligned on their respective natural boundaries (and initialized using memcpy). PR 29856 libsframe asan: load misaligned at sframe.c:516 ChangeLog: PR libsframe/29856 * bfd/elf64-x86-64.c: Adjust as the struct members have been reordered. * libsframe/sframe.c (sframe_decode_fre_start_address): Use memcpy to perform 16-bit/32-bit reads. * libsframe/testsuite/libsframe.encode/encode-1.c: Adjust as the struct members have been reordered. include/ChangeLog: PR libsframe/29856 * sframe-api.h: Reorder fre_offsets for natural alignment. --- bfd/elf64-x86-64.c | 24 +++++++++---------- include/sframe-api.h | 8 +++++-- libsframe/sframe.c | 18 ++++++++++++-- .../testsuite/libsframe.encode/encode-1.c | 16 ++++++------- 4 files changed, 42 insertions(+), 24 deletions(-) diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c index afc8c76c52b..8cf733d89e0 100644 --- a/bfd/elf64-x86-64.c +++ b/bfd/elf64-x86-64.c @@ -822,48 +822,48 @@ static const bfd_byte elf_x86_64_eh_frame_non_lazy_plt[] = static const sframe_frame_row_entry elf_x86_64_sframe_null_fre = { 0, - SFRAME_V1_FRE_INFO (SFRAME_BASE_REG_SP, 1, SFRAME_FRE_OFFSET_1B), /* FRE info. */ - {16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0} /* 12 bytes. */ + {16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, /* 12 bytes. */ + SFRAME_V1_FRE_INFO (SFRAME_BASE_REG_SP, 1, SFRAME_FRE_OFFSET_1B) /* FRE info. */ }; /* .sframe FRE covering the .plt section entry. */ static const sframe_frame_row_entry elf_x86_64_sframe_plt0_fre1 = { 0, /* SFrame FRE start address. */ - SFRAME_V1_FRE_INFO (SFRAME_BASE_REG_SP, 1, SFRAME_FRE_OFFSET_1B), /* FRE info. */ - {16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0} /* 12 bytes. */ + {16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, /* 12 bytes. */ + SFRAME_V1_FRE_INFO (SFRAME_BASE_REG_SP, 1, SFRAME_FRE_OFFSET_1B) /* FRE info. */ }; /* .sframe FRE covering the .plt section entry. */ static const sframe_frame_row_entry elf_x86_64_sframe_plt0_fre2 = { 6, /* SFrame FRE start address. */ - SFRAME_V1_FRE_INFO (SFRAME_BASE_REG_SP, 1, SFRAME_FRE_OFFSET_1B), /* FRE info. */ - {24, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0} /* 12 bytes. */ + {24, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, /* 12 bytes. */ + SFRAME_V1_FRE_INFO (SFRAME_BASE_REG_SP, 1, SFRAME_FRE_OFFSET_1B) /* FRE info. */ }; /* .sframe FRE covering the .plt section entry. */ static const sframe_frame_row_entry elf_x86_64_sframe_pltn_fre1 = { 0, /* SFrame FRE start address. */ - SFRAME_V1_FRE_INFO (SFRAME_BASE_REG_SP, 1, SFRAME_FRE_OFFSET_1B), /* FRE info. */ - {8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0} /* 12 bytes. */ + {8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, /* 12 bytes. */ + SFRAME_V1_FRE_INFO (SFRAME_BASE_REG_SP, 1, SFRAME_FRE_OFFSET_1B) /* FRE info. */ }; /* .sframe FRE covering the .plt section entry. */ static const sframe_frame_row_entry elf_x86_64_sframe_pltn_fre2 = { 11, /* SFrame FRE start address. */ - SFRAME_V1_FRE_INFO (SFRAME_BASE_REG_SP, 1, SFRAME_FRE_OFFSET_1B), /* FRE info. */ - {16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0} /* 12 bytes. */ + {16, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, /* 12 bytes. */ + SFRAME_V1_FRE_INFO (SFRAME_BASE_REG_SP, 1, SFRAME_FRE_OFFSET_1B) /* FRE info. */ }; /* .sframe FRE covering the second .plt section entry. */ static const sframe_frame_row_entry elf_x86_64_sframe_sec_pltn_fre1 = { 0, /* SFrame FRE start address. */ - SFRAME_V1_FRE_INFO (SFRAME_BASE_REG_SP, 1, SFRAME_FRE_OFFSET_1B), /* FRE info. */ - {8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0} /* 12 bytes. */ + {8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, /* 12 bytes. */ + SFRAME_V1_FRE_INFO (SFRAME_BASE_REG_SP, 1, SFRAME_FRE_OFFSET_1B) /* FRE info. */ }; /* SFrame helper object for non-lazy PLT. Also used for IBT enabled PLT. */ diff --git a/include/sframe-api.h b/include/sframe-api.h index 0a86389857c..c9db39eaaf0 100644 --- a/include/sframe-api.h +++ b/include/sframe-api.h @@ -34,13 +34,17 @@ typedef struct sframe_encoder_ctx sframe_encoder_ctx; /* User interfacing SFrame Row Entry. An abstraction provided by libsframe so the consumer is decoupled from - the binary format representation of the same. */ + the binary format representation of the same. + + The members are best ordered such that they are aligned at their natural + boundaries. This helps avoid usage of undesirable misaligned memory + accesses. See PR libsframe/29856. */ typedef struct sframe_frame_row_entry { uint32_t fre_start_addr; - unsigned char fre_info; unsigned char fre_offsets[MAX_OFFSET_BYTES]; + unsigned char fre_info; } sframe_frame_row_entry; #define SFRAME_ERR ((int) -1) diff --git a/libsframe/sframe.c b/libsframe/sframe.c index d4eaaee2297..b17d3234236 100644 --- a/libsframe/sframe.c +++ b/libsframe/sframe.c @@ -652,6 +652,11 @@ sframe_frame_row_entry_copy (sframe_frame_row_entry *dst, sframe_frame_row_entry return 0; } +/* Decode the SFrame FRE start address offset value from FRE_BUF in on-disk + binary format, given the FRE_TYPE. Updates the FRE_START_ADDR. + + Returns 0 on success, SFRAME_ERR otherwise. */ + static int sframe_decode_fre_start_address (const char *fre_buf, uint32_t *fre_start_addr, @@ -659,6 +664,9 @@ sframe_decode_fre_start_address (const char *fre_buf, { uint32_t saddr = 0; int err = 0; + size_t addr_size = 0; + + addr_size = sframe_fre_start_addr_size (fre_type); if (fre_type == SFRAME_FRE_TYPE_ADDR1) { @@ -668,12 +676,18 @@ sframe_decode_fre_start_address (const char *fre_buf, else if (fre_type == SFRAME_FRE_TYPE_ADDR2) { uint16_t *ust = (uint16_t *)fre_buf; - saddr = (uint32_t)*ust; + /* SFrame is an unaligned on-disk format. Using memcpy helps avoid the + use of undesirable unaligned loads. See PR libsframe/29856. */ + uint16_t tmp = 0; + memcpy (&tmp, ust, addr_size); + saddr = (uint32_t)tmp; } else if (fre_type == SFRAME_FRE_TYPE_ADDR4) { uint32_t *uit = (uint32_t *)fre_buf; - saddr = (uint32_t)*uit; + int32_t tmp = 0; + memcpy (&tmp, uit, addr_size); + saddr = (uint32_t)tmp; } else return sframe_set_errno (&err, SFRAME_ERR_INVAL); diff --git a/libsframe/testsuite/libsframe.encode/encode-1.c b/libsframe/testsuite/libsframe.encode/encode-1.c index 01481106a62..0f5225ff9ec 100644 --- a/libsframe/testsuite/libsframe.encode/encode-1.c +++ b/libsframe/testsuite/libsframe.encode/encode-1.c @@ -33,10 +33,10 @@ add_fde1 (sframe_encoder_ctx *encode, int idx) int i, err; /* A contiguous block containing 4 FREs. */ sframe_frame_row_entry fres[] - = { {0x0, 0x3, {0x8, 0, 0}}, - {0x1, 0x5, {0x10, 0xf0, 0}}, - {0x4, 0x4, {0x10, 0xf0, 0}}, - {0x1a, 0x5, {0x8, 0xf0, 0}} + = { {0x0, {0x8, 0, 0}, 0x3}, + {0x1, {0x10, 0xf0, 0}, 0x5}, + {0x4, {0x10, 0xf0, 0}, 0x4}, + {0x1a, {0x8, 0xf0, 0}, 0x5} }; unsigned char finfo = sframe_fde_create_func_info (SFRAME_FRE_TYPE_ADDR1, @@ -58,10 +58,10 @@ add_fde2 (sframe_encoder_ctx *encode, int idx) int i, err; /* A contiguous block containing 4 FREs. */ sframe_frame_row_entry fres[] - = { {0x0, 0x3, {0x8, 0, 0}}, - {0x1, 0x5, {0x10, 0xf0, 0}}, - {0x4, 0x4, {0x10, 0xf0, 0}}, - {0xf, 0x5, {0x8, 0xf0, 0}} + = { {0x0, {0x8, 0, 0}, 0x3}, + {0x1, {0x10, 0xf0, 0}, 0x5}, + {0x4, {0x10, 0xf0, 0}, 0x4}, + {0xf, {0x8, 0xf0, 0}, 0x5} }; unsigned char finfo = sframe_fde_create_func_info (SFRAME_FRE_TYPE_ADDR1, -- 2.30.2