On Fri, May 21, 2021 at 03:46:20PM +0100, Mark Brown wrote:
> Currently the ELF code only attempts to parse properties on the image
> that will start execution, either the interpreter or for statically linked
> executables the main executable. The expectation is that any property
> handling for the main executable will be done by the interpreter. This is
> a bit inconsistent since we do map the executable and is causing problems
> for the arm64 BTI support when used in conjunction with systemd's use of
> seccomp to implement MemoryDenyWriteExecute which stops the dynamic linker
> adjusting the permissions of executable segments.
>
> Allow architectures to handle properties for both the dynamic linker and
> main executable, adjusting arch_parse_elf_properties() to have an is_interp
> flag as with arch_elf_adjust_prot() and calling it for both the main
> executable and any intepreter.
>
> Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
> ---
> arch/arm64/include/asm/elf.h | 3 ++-
> fs/binfmt_elf.c | 25 +++++++++++++++++--------
> include/linux/elf.h | 4 +++-
> 3 files changed, 22 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
> index 8d1c8dcb87fd..c8678a8c36d5 100644
> --- a/arch/arm64/include/asm/elf.h
> +++ b/arch/arm64/include/asm/elf.h
> @@ -261,6 +261,7 @@ struct arch_elf_state {
>
> static inline int arch_parse_elf_property(u32 type, const void *data,
> size_t datasz, bool compat,
> + bool is_interp,
> struct arch_elf_state *arch)
> {
> /* No known properties for AArch32 yet */
> @@ -273,7 +274,7 @@ static inline int arch_parse_elf_property(u32 type, const void *data,
> if (datasz != sizeof(*p))
> return -ENOEXEC;
>
> - if (system_supports_bti() &&
> + if (system_supports_bti() && is_interp &&
Won't this cause BTI to be forced off for static binaries?
Perhaps this should be (has_interp == is_interp), as for
arch_elf_adjust_prot(). Seems gross though, since has_interp would
become useless after the next patch. If there's no sensible way to
keep this bisectable, perhaps the patches can be merged instead.
(has_interp should probably also go away for arch_elf_adjust_prot() --
see my comments on the next patch).
> (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI))
> arch->flags |= ARM64_ELF_BTI;
> }
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 187b3f2b9202..c8397664af39 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -716,7 +716,7 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
> */
>
> static int parse_elf_property(const char *data, size_t *off, size_t datasz,
> - struct arch_elf_state *arch,
> + struct arch_elf_state *arch, bool is_interp,
> bool have_prev_type, u32 *prev_type)
> {
> size_t o, step;
> @@ -751,7 +751,8 @@ static int parse_elf_property(const char *data, size_t *off, size_t datasz,
> *prev_type = pr->pr_type;
>
> ret = arch_parse_elf_property(pr->pr_type, data + o,
> - pr->pr_datasz, ELF_COMPAT, arch);
> + pr->pr_datasz, ELF_COMPAT, is_interp,
> + arch);
> if (ret)
> return ret;
>
> @@ -764,7 +765,7 @@ static int parse_elf_property(const char *data, size_t *off, size_t datasz,
> #define NOTE_NAME_SZ (sizeof(GNU_PROPERTY_TYPE_0_NAME))
>
> static int parse_elf_properties(struct file *f, const struct elf_phdr *phdr,
> - struct arch_elf_state *arch)
> + bool is_interp, struct arch_elf_state *arch)
> {
> union {
> struct elf_note nhdr;
> @@ -813,7 +814,8 @@ static int parse_elf_properties(struct file *f, const struct elf_phdr *phdr,
> have_prev_type = false;
> do {
> ret = parse_elf_property(note.data, &off, datasz, arch,
> - have_prev_type, &prev_type);
> + is_interp, have_prev_type,
> + &prev_type);
> have_prev_type = true;
> } while (!ret);
>
> @@ -828,6 +830,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
> unsigned long error;
> struct elf_phdr *elf_ppnt, *elf_phdata, *interp_elf_phdata = NULL;
> struct elf_phdr *elf_property_phdata = NULL;
> + struct elf_phdr *interp_elf_property_phdata = NULL;
> unsigned long elf_bss, elf_brk;
> int bss_prot = 0;
> int retval, i;
> @@ -963,12 +966,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
> goto out_free_dentry;
>
> /* Pass PT_LOPROC..PT_HIPROC headers to arch code */
> - elf_property_phdata = NULL;
> elf_ppnt = interp_elf_phdata;
> for (i = 0; i < interp_elf_ex->e_phnum; i++, elf_ppnt++)
> switch (elf_ppnt->p_type) {
> case PT_GNU_PROPERTY:
> - elf_property_phdata = elf_ppnt;
> + interp_elf_property_phdata = elf_ppnt;
(Hmm, this actually looks a bit cleaner than just clobbering
elf_property_phdata with the interpreter properties as was done
previously.)
> break;
>
> case PT_LOPROC ... PT_HIPROC:
> @@ -979,10 +981,17 @@ static int load_elf_binary(struct linux_binprm *bprm)
> goto out_free_dentry;
> break;
> }
> +
> + retval = parse_elf_properties(interpreter,
> + interp_elf_property_phdata,
> + true, &arch_state);
> + if (retval)
> + goto out_free_dentry;
> +
> }
>
> - retval = parse_elf_properties(interpreter ?: bprm->file,
> - elf_property_phdata, &arch_state);
> + retval = parse_elf_properties(bprm->file, elf_property_phdata,
> + false, &arch_state);
> if (retval)
> goto out_free_dentry;
>
> diff --git a/include/linux/elf.h b/include/linux/elf.h
> index c9a46c4e183b..a20dcdcd86c5 100644
> --- a/include/linux/elf.h
> +++ b/include/linux/elf.h
> @@ -88,13 +88,15 @@ struct arch_elf_state;
> #ifndef CONFIG_ARCH_USE_GNU_PROPERTY
> static inline int arch_parse_elf_property(u32 type, const void *data,
> size_t datasz, bool compat,
> + bool is_interp,
> struct arch_elf_state *arch)
> {
> return 0;
> }
> #else
> extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
> - bool compat, struct arch_elf_state *arch);
> + bool compat, bool is_interp,
> + struct arch_elf_state *arch);
> #endif
Looks like a sensible change, modulo my comments above.
You may want to Cc Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> when reposting,
since this would affect his patches (trivially though).
Cheers
---Dave
