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Message-ID: <CAMj1kXHoiF_OZxVgrBXCQ=Uqa+TUCC=d33Ep4V9hB5kESs=ijg@mail.gmail.com>
Date: Sat, 3 May 2025 13:45:57 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
will@...nel.org, catalin.marinas@....com, mark.rutland@....com,
Yeoreum Yun <yeoreum.yun@....com>
Subject: Re: [PATCH 3/3] arm64/boot: Disallow BSS exports to startup code
On Sat, 3 May 2025 at 13:22, Ard Biesheuvel <ardb+git@...gle.com> wrote:
>
> From: Ard Biesheuvel <ardb@...nel.org>
>
> BSS might be uninitialized when entering the startup code, so forbid the
> use of any variables that live after __bss_start in the linker map.
>
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> ---
> arch/arm64/kernel/image-vars.h | 66 +++++++++++---------
> arch/arm64/kernel/vmlinux.lds.S | 2 +
> 2 files changed, 37 insertions(+), 31 deletions(-)
>
> diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
> index a0977f7cd3ec..a70244d1aa2a 100644
> --- a/arch/arm64/kernel/image-vars.h
> +++ b/arch/arm64/kernel/image-vars.h
> @@ -10,6 +10,12 @@
> #error This file should only be included in vmlinux.lds.S
> #endif
>
> +#define PI_EXPORT_SYM(sym) \
> + __PI_EXPORT_SYM(sym, __pi_ ## sym, Cannot export BSS symbol sym to startup code)
> +#define __PI_EXPORT_SYM(sym, pisym, msg)\
> + PROVIDE(pisym = sym); \
> + ASSERT(sym < __bss_start, #msg)
LLD doesn't seem to love this. I'll replace this with
ASSERT((sym - KIMAGE_VADDR) < (__bss_start - KIMAGE_VADDR), #msg)
which appears to work for both LLD and ld.bfd
> +
> PROVIDE(__efistub_primary_entry = primary_entry);
>
> /*
> @@ -36,39 +42,37 @@ PROVIDE(__pi___memcpy = __pi_memcpy);
> PROVIDE(__pi___memmove = __pi_memmove);
> PROVIDE(__pi___memset = __pi_memset);
>
> -PROVIDE(__pi_id_aa64isar1_override = id_aa64isar1_override);
> -PROVIDE(__pi_id_aa64isar2_override = id_aa64isar2_override);
> -PROVIDE(__pi_id_aa64mmfr0_override = id_aa64mmfr0_override);
> -PROVIDE(__pi_id_aa64mmfr1_override = id_aa64mmfr1_override);
> -PROVIDE(__pi_id_aa64mmfr2_override = id_aa64mmfr2_override);
> -PROVIDE(__pi_id_aa64pfr0_override = id_aa64pfr0_override);
> -PROVIDE(__pi_id_aa64pfr1_override = id_aa64pfr1_override);
> -PROVIDE(__pi_id_aa64smfr0_override = id_aa64smfr0_override);
> -PROVIDE(__pi_id_aa64zfr0_override = id_aa64zfr0_override);
> -PROVIDE(__pi_arm64_sw_feature_override = arm64_sw_feature_override);
> -PROVIDE(__pi_arm64_use_ng_mappings = arm64_use_ng_mappings);
> +PI_EXPORT_SYM(id_aa64isar1_override);
> +PI_EXPORT_SYM(id_aa64isar2_override);
> +PI_EXPORT_SYM(id_aa64mmfr0_override);
> +PI_EXPORT_SYM(id_aa64mmfr1_override);
> +PI_EXPORT_SYM(id_aa64mmfr2_override);
> +PI_EXPORT_SYM(id_aa64pfr0_override);
> +PI_EXPORT_SYM(id_aa64pfr1_override);
> +PI_EXPORT_SYM(id_aa64smfr0_override);
> +PI_EXPORT_SYM(id_aa64zfr0_override);
> +PI_EXPORT_SYM(arm64_sw_feature_override);
> +PI_EXPORT_SYM(arm64_use_ng_mappings);
> #ifdef CONFIG_CAVIUM_ERRATUM_27456
> -PROVIDE(__pi_cavium_erratum_27456_cpus = cavium_erratum_27456_cpus);
> -PROVIDE(__pi_is_midr_in_range_list = is_midr_in_range_list);
> +PI_EXPORT_SYM(cavium_erratum_27456_cpus);
> +PI_EXPORT_SYM(is_midr_in_range_list);
> #endif
> -PROVIDE(__pi__ctype = _ctype);
> -PROVIDE(__pi_memstart_offset_seed = memstart_offset_seed);
> -
> -PROVIDE(__pi_init_idmap_pg_dir = init_idmap_pg_dir);
> -PROVIDE(__pi_init_idmap_pg_end = init_idmap_pg_end);
> -PROVIDE(__pi_swapper_pg_dir = swapper_pg_dir);
> -
> -PROVIDE(__pi__text = _text);
> -PROVIDE(__pi__stext = _stext);
> -PROVIDE(__pi__etext = _etext);
> -PROVIDE(__pi___start_rodata = __start_rodata);
> -PROVIDE(__pi___inittext_begin = __inittext_begin);
> -PROVIDE(__pi___inittext_end = __inittext_end);
> -PROVIDE(__pi___initdata_begin = __initdata_begin);
> -PROVIDE(__pi___initdata_end = __initdata_end);
> -PROVIDE(__pi__data = _data);
> -PROVIDE(__pi___bss_start = __bss_start);
> -PROVIDE(__pi__end = _end);
> +PI_EXPORT_SYM(_ctype);
> +PI_EXPORT_SYM(memstart_offset_seed);
> +
> +PI_EXPORT_SYM(init_idmap_pg_dir);
> +PI_EXPORT_SYM(init_idmap_pg_end);
> +PI_EXPORT_SYM(swapper_pg_dir);
> +
> +PI_EXPORT_SYM(_text);
> +PI_EXPORT_SYM(_stext);
> +PI_EXPORT_SYM(_etext);
> +PI_EXPORT_SYM(__start_rodata);
> +PI_EXPORT_SYM(__inittext_begin);
> +PI_EXPORT_SYM(__inittext_end);
> +PI_EXPORT_SYM(__initdata_begin);
> +PI_EXPORT_SYM(__initdata_end);
> +PI_EXPORT_SYM(_data);
>
> #ifdef CONFIG_KVM
>
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index 73fa57f341b0..bd7626b8c7a3 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -319,6 +319,7 @@ SECTIONS
>
> /* start of zero-init region */
> BSS_SECTION(SBSS_ALIGN, 0, 0)
> + __pi___bss_start = __bss_start;
>
> . = ALIGN(PAGE_SIZE);
> __pi_init_pg_dir = .;
> @@ -332,6 +333,7 @@ SECTIONS
> . = ALIGN(SEGMENT_ALIGN);
> __pecoff_data_size = ABSOLUTE(. - __initdata_begin);
> _end = .;
> + __pi__end = .;
>
> STABS_DEBUG
> DWARF_DEBUG
> --
> 2.49.0.906.g1f30a19c02-goog
>
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