[PATCH V4 8/8] ld/aarch64elf: add support for DT_AARCH64_MEMTAG_STACK dynamic tag
Richard Earnshaw
Richard.Earnshaw@arm.com
Fri Jul 11 14:01:38 GMT 2025
On 09/07/2025 22:44, Jose E. Marchesi via Binutils wrote:
> From: Indu Bhagat <indu.bhagat@oracle.com>
>
> Add new command line option -z memtag-stack for aarch64 elf. This
> option instructs the linker to generate the necessary dynamic tag
> DT_AARCH64_MEMTAG_STACK, which the dynamic loader can then use to
> protect the stack memory with PROT_MTE. Linker issues an
> 'unrecognized option' error when -z memtag-stack is specified for
> non-aarch64 based emulations.
>
> readelf displays the dynamic tag when present:
>
> $ readelf -d <exectutable>
> Dynamic section at offset 0xfdd8 contains XX entries:
> Tag Type Name/Value
> 0x0000000000000001 (NEEDED) Shared library: [libc.so.6]
> 0x000000000000000c (INIT) 0x400520
> 0x000000000000000d (FINI) 0x400b64
> 0x0000000000000019 (INIT_ARRAY) 0x41fdc8
> ... ... ...
> 0x000000007000000c (AARCH64_MEMTAG_STACK) 0x1
> ... ... ...
>
> ChangeLog:
>
> * bfd/elfnn-aarch64.c (elfNN_aarch64_late_size_sections): Emit
> DT_AARCH64_MEMTAG_STACK dynamic tag.
> * bfd/elfxx-aarch64.h (struct aarch64_memtag_opts): Add new
> member for tracking whether stack access uses MTE insns.
> * binutils/readelf.c (get_aarch64_dynamic_type): Handle
> DT_AARCH64_MEMTAG_STACK.
> * ld/emultempl/aarch64elf.em: Add new command line option.
> * ld/ld.texi: Add documentation for -z memtag-stack.
> * ld/testsuite/ld-aarch64/aarch64-elf.exp: Add new test.
> * ld/testsuite/ld-aarch64/dt-memtag-stack.d: New test.
>
> include/ChangeLog:
>
> * elf/aarch64.h (DT_AARCH64_MEMTAG_STACK): New definition.
> ---
> bfd/elfnn-aarch64.c | 6 ++++++
> bfd/elfxx-aarch64.h | 3 +++
> binutils/readelf.c | 1 +
> include/elf/aarch64.h | 1 +
> ld/emultempl/aarch64elf.em | 5 +++++
> ld/ld.texi | 5 +++++
> ld/testsuite/ld-aarch64/aarch64-elf.exp | 1 +
> ld/testsuite/ld-aarch64/dt-memtag-stack.d | 7 +++++++
> 8 files changed, 29 insertions(+)
> create mode 100644 ld/testsuite/ld-aarch64/dt-memtag-stack.d
>
> diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
> index 0e9e22e210b..9e98215d638 100644
> --- a/bfd/elfnn-aarch64.c
> +++ b/bfd/elfnn-aarch64.c
> @@ -9786,6 +9786,12 @@ elfNN_aarch64_late_size_sections (bfd *output_bfd ATTRIBUTE_UNUSED,
> && !add_dynamic_entry (DT_AARCH64_MEMTAG_MODE,
> htab->memtag_opts.memtag_mode == AARCH64_MEMTAG_MODE_ASYNC))
> return false;
> +
> + if (is_aarch64_elf (output_bfd)
> + && htab->memtag_opts.memtag_stack == 1
> + && !add_dynamic_entry (DT_AARCH64_MEMTAG_STACK,
> + htab->memtag_opts.memtag_stack == 1))
> + return false;
> }
>
> #undef add_dynamic_entry
> diff --git a/bfd/elfxx-aarch64.h b/bfd/elfxx-aarch64.h
> index 66c1f48d450..bd3642cbefe 100644
> --- a/bfd/elfxx-aarch64.h
> +++ b/bfd/elfxx-aarch64.h
> @@ -147,6 +147,9 @@ struct aarch64_memtag_opts
> {
> /* Mode of MTE operation. */
> aarch64_memtag_mode_type memtag_mode;
> +
> + /* Whether stack accesses use MTE insns. */
> + unsigned int memtag_stack;
> };
>
> typedef struct aarch64_memtag_opts aarch64_memtag_opts;
> diff --git a/binutils/readelf.c b/binutils/readelf.c
> index 2ae6eea810f..e1964906661 100644
> --- a/binutils/readelf.c
> +++ b/binutils/readelf.c
> @@ -2588,6 +2588,7 @@ get_aarch64_dynamic_type (unsigned long type)
> case DT_AARCH64_PAC_PLT: return "AARCH64_PAC_PLT";
> case DT_AARCH64_VARIANT_PCS: return "AARCH64_VARIANT_PCS";
> case DT_AARCH64_MEMTAG_MODE: return "AARCH64_MEMTAG_MODE";
> + case DT_AARCH64_MEMTAG_STACK: return "AARCH64_MEMTAG_STACK";
>
> default:
> return NULL;
> diff --git a/include/elf/aarch64.h b/include/elf/aarch64.h
> index 129aef9a524..a4ef1118402 100644
> --- a/include/elf/aarch64.h
> +++ b/include/elf/aarch64.h
> @@ -53,6 +53,7 @@
> #define DT_AARCH64_PAC_PLT (DT_LOPROC + 3)
> #define DT_AARCH64_VARIANT_PCS (DT_LOPROC + 5)
> #define DT_AARCH64_MEMTAG_MODE (DT_LOPROC + 9)
> +#define DT_AARCH64_MEMTAG_STACK (DT_LOPROC + 12)
>
> /* AArch64-specific values for st_other. */
> #define STO_AARCH64_VARIANT_PCS 0x80 /* Symbol may follow different call
> diff --git a/ld/emultempl/aarch64elf.em b/ld/emultempl/aarch64elf.em
> index d7e4eb78059..66eaf1cd861 100644
> --- a/ld/emultempl/aarch64elf.em
> +++ b/ld/emultempl/aarch64elf.em
> @@ -44,6 +44,7 @@ static aarch64_protection_opts sw_protections = {
>
> static aarch64_memtag_opts memtag_opts = {
> .memtag_mode = AARCH64_MEMTAG_MODE_NONE,
> + .memtag_stack = 0,
> };
>
> #define COMPILE_TIME_STRLEN(s) \
> @@ -557,6 +558,8 @@ PARSE_AND_LIST_OPTIONS='
> sync: Enable precise exceptions when mismatched address and\n\
> allocation tags detected on load/store operations.\n\
> async: Enable imprecise exceptions.\n"));
> + fprintf (file, _("\
> + -z memtag-stack Mark program stack with MTE protection.\n"));
> '
>
> PARSE_AND_LIST_ARGS_CASE_Z_AARCH64='
> @@ -574,6 +577,8 @@ PARSE_AND_LIST_ARGS_CASE_Z_AARCH64='
> {}
> else if (aarch64_parse_memtag_mode_option (optarg))
> {}
> + else if (strcmp (optarg, "memtag-stack") == 0)
> + memtag_opts.memtag_stack = 1;
> '
> PARSE_AND_LIST_ARGS_CASE_Z="$PARSE_AND_LIST_ARGS_CASE_Z $PARSE_AND_LIST_ARGS_CASE_Z_AARCH64"
>
> diff --git a/ld/ld.texi b/ld/ld.texi
> index f196f1e5870..4460a084404 100644
> --- a/ld/ld.texi
> +++ b/ld/ld.texi
> @@ -8383,6 +8383,11 @@ dynamic tag. The @samp{sync} mode implies precise exceptions, with the runtime
> providing the exact instruction where the fault occurred, and the exact
> faulting address. The @samp{async} mode implies imprecise exceptions.
>
> +@kindex -z memtag-stack
> +@cindex Mark program stack for MTE protection
> +The @samp{-z memtag-stack} specifies that output object uses MTE
> +instructions for stack memory usage.
> +
> @ifclear GENERIC
> @lowersections
> @end ifclear
> diff --git a/ld/testsuite/ld-aarch64/aarch64-elf.exp b/ld/testsuite/ld-aarch64/aarch64-elf.exp
> index 56e68c584fb..8d56beb64c7 100644
> --- a/ld/testsuite/ld-aarch64/aarch64-elf.exp
> +++ b/ld/testsuite/ld-aarch64/aarch64-elf.exp
> @@ -378,6 +378,7 @@ run_dump_test_lp64 "variant_pcs-now"
>
> run_dump_test_lp64 "mte-tagged-frame"
> run_dump_test_lp64 "dt-memtag-mode"
> +run_dump_test_lp64 "dt-memtag-stack"
>
> set aarch64elflinktests {
> {"ld-aarch64/so with global symbol" "-shared" "" "" {copy-reloc-so.s}
> diff --git a/ld/testsuite/ld-aarch64/dt-memtag-stack.d b/ld/testsuite/ld-aarch64/dt-memtag-stack.d
> new file mode 100644
> index 00000000000..242f61fa172
> --- /dev/null
> +++ b/ld/testsuite/ld-aarch64/dt-memtag-stack.d
> @@ -0,0 +1,7 @@
> +#source: dt-memtag.s
> +#ld: -shared -z memtag-stack
> +#readelf: -d
> +
> +#...
> + 0x000000007000000c \(AARCH64_MEMTAG_STACK\) 0x1
> +#...
OK
R
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