[PATCH] riscv: elf: add .riscv.attributes parsing
Jessica Clarke
jrtc27 at jrtc27.com
Tue Jan 10 12:48:03 PST 2023
On 10 Jan 2023, at 20:18, Vineet Gupta <vineetg at rivosinc.com> wrote:
>
> This implements the elf loader hook to parse RV specific
> .riscv.attributes section. This section is inserted by compilers
> (gcc/llvm) with build related information such as -march organized as
> tag/value attribute pairs.
>
> It identifies the various attribute tags (and corresponding values) as
> currently specified in the psABI specification.
>
> This patch only implements the elf parsing mechanics, leaving out the
> recording/usage of the attributes to subsequent patches.
>
> Reported-by: kernel test robot <lkp at intel.com> # code under CONFIG_COMPAT
> Signed-off-by: Vineet Gupta <vineetg at rivosinc.com>
This code is full of buffer overruns and uninitialised reads in the
presence of malicious files, and fails to check the version, vendor and
sub-subsection tag.
You also should handle more than one sub-subsection even if tools don’t
emit it today.
You also have an unaligned access for reading the sub-subsection’s data
length (maybe that’s ok in kernel land, but worth making sure).
Jess
> ---
> arch/riscv/Kconfig | 1 +
> arch/riscv/include/asm/elf.h | 11 +++
> arch/riscv/kernel/Makefile | 1 +
> arch/riscv/kernel/elf-attr.c | 150 +++++++++++++++++++++++++++++++++++
> 4 files changed, 163 insertions(+)
> create mode 100644 arch/riscv/kernel/elf-attr.c
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index e2b656043abf..f7e0ab05a2d2 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -12,6 +12,7 @@ config 32BIT
>
> config RISCV
> def_bool y
> + select ARCH_BINFMT_ELF_STATE
> select ARCH_CLOCKSOURCE_INIT
> select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION
> select ARCH_ENABLE_SPLIT_PMD_PTLOCK if PGTABLE_LEVELS > 2
> diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
> index e7acffdf21d2..7ab8bd0ec330 100644
> --- a/arch/riscv/include/asm/elf.h
> +++ b/arch/riscv/include/asm/elf.h
> @@ -116,6 +116,17 @@ do { \
> *(struct user_regs_struct *)regs; \
> } while (0);
>
> +struct arch_elf_state {
> +};
> +
> +#define INIT_ARCH_ELF_STATE {}
> +
> +extern int arch_elf_pt_proc(void *ehdr, void *phdr, struct file *elf,
> + bool is_interp, struct arch_elf_state *state);
> +
> +extern int arch_check_elf(void *ehdr, bool has_interpreter, void *interp_ehdr,
> + struct arch_elf_state *state);
> +
> #ifdef CONFIG_COMPAT
>
> #define SET_PERSONALITY(ex) \
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index 4cf303a779ab..eff6d845ac9d 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -50,6 +50,7 @@ obj-y += riscv_ksyms.o
> obj-y += stacktrace.o
> obj-y += cacheinfo.o
> obj-y += patch.o
> +obj-y += elf-attr.o
> obj-y += probes/
> obj-$(CONFIG_MMU) += vdso.o vdso/
>
> diff --git a/arch/riscv/kernel/elf-attr.c b/arch/riscv/kernel/elf-attr.c
> new file mode 100644
> index 000000000000..148d720f97de
> --- /dev/null
> +++ b/arch/riscv/kernel/elf-attr.c
> @@ -0,0 +1,150 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2023-24 Rivos Inc.
> + */
> +
> +#include <linux/binfmts.h>
> +#include <linux/elf.h>
> +
> +#undef pr_fmt
> +#define pr_fmt(fmt) "rv-elf-attr: " fmt
> +
> +#define PT_RISCV_ATTRIBUTES 0x70000003
> +
> +#define RV_ATTR_TAG_stack_align 4
> +#define RV_ATTR_TAG_arch 5
> +#define RV_ATTR_TAG_unaligned_access 6
> +
> +#define RV_ATTR_SEC_SZ SZ_1K
> +
> +static void rv_elf_attr_int(u64 tag, u64 val)
> +{
> +}
> +
> +static void rv_elf_attr_str(u64 tag, const char *str)
> +{
> +}
> +
> +static u64
> +decode_uleb128(unsigned char **dpp)
> +{
> + unsigned char *bp = *dpp;
> + unsigned char byte;
> + unsigned int shift = 0;
> + u64 result = 0;
> +
> + while (1) {
> + byte = *bp++;
> + result |= (byte & 0x7f) << shift;
> + if ((byte & 0x80) == 0)
> + break;
> + shift += 7;
> + }
> + *dpp = bp;
> + return result;
> +}
> +
> +/*
> + * Parse .riscv.attributes elf section to get the various compile time
> + * attributes such as -march, unaligned access and so no.
> + */
> +static int rv_parse_elf_attributes(struct file *f, const struct elf_phdr *phdr,
> + struct arch_elf_state *state)
> +{
> + unsigned char buf[RV_ATTR_SEC_SZ];
> + unsigned char *p;
> + ssize_t n;
> + int ret = 0;
> + loff_t pos;
> +
> + pr_debug("Section .riscv.attributes found\n");
> +
> + /* Assume a reasonable size for now */
> + if (phdr->p_filesz > sizeof(buf))
> + return -ENOEXEC;
> +
> + memset(buf, 0, RV_ATTR_SEC_SZ);
> + pos = phdr->p_offset;
> + n = kernel_read(f, &buf, phdr->p_filesz, &pos);
> +
> + if (n < 0)
> + return -EIO;
> +
> + p = buf;
> + p++; /* format-version (1B) */
> +
> + while ((p - buf) < n) {
> +
> + unsigned char *vendor_start;
> + u32 len;
> +
> + /*
> + * Organized as "vendor" sub-section(s).
> + * Current only 1 specified "riscv"
> + */
> +
> + p += 4; /* sub-section length (4B) */
> + while (*p++ != '\0') /* vendor name string */
> + ;
> + p++; /* Tag_File (1B) */
> + len = *(u32 *)p; /* data length (4B) */
> + p += 4;
> +
> + len -= 5; /* data length includes Tag and self length */
> + vendor_start = p;
> + while ((p - vendor_start) < len) {
> +
> + u64 tag = decode_uleb128(&p);
> + unsigned char *val_str;
> + u64 val_n;
> +
> + switch (tag) {
> + case RV_ATTR_TAG_stack_align:
> + val_n = decode_uleb128(&p);
> + break;
> +
> + case RV_ATTR_TAG_unaligned_access:
> + val_n = decode_uleb128(&p);
> + pr_debug("Tag_RISCV_unaligned_access =%llu\n", val_n);
> + rv_elf_attr_int(tag, val_n);
> + break;
> +
> + case RV_ATTR_TAG_arch:
> + val_str = p;
> + while (*p++ != '\0')
> + ;
> + pr_debug("Tag_RISCV_arch =[%s]\n", val_str);
> + rv_elf_attr_str(tag, val_str);
> + break;
> +
> + default:
> + val_n = decode_uleb128(&p);
> + pr_debug("skipping Unrecognized Tag [%llu]=%llu\n", tag, val_n);
> + break;
> + }
> + }
> + }
> +
> + return ret;
> +}
> +
> +/*
> + * Hook invoked from common elf loader to parse any arch specific elf segments
> + */
> +int arch_elf_pt_proc(void *_ehdr, void *_phdr, struct file *elf,
> + bool is_interp, struct arch_elf_state *state)
> +{
> + struct elf_phdr *phdr = _phdr;
> + int ret = 0;
> +
> + if (phdr->p_type == PT_RISCV_ATTRIBUTES && !is_interp)
> + ret = rv_parse_elf_attributes(elf, phdr, state);
> +
> + return ret;
> +}
> +
> +int arch_check_elf(void *_ehdr, bool has_interpreter, void *_interp_ehdr,
> + struct arch_elf_state *state)
> +{
> + return 0;
> +}
> --
> 2.34.1
>
>
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