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SubjectRe: [PATCH 4/5] efi/x86: Remove extra headroom for setup block
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On 2.3.2020 1.05, Arvind Sankar wrote:
> commit 223e3ee56f77 ("efi/x86: add headroom to decompressor BSS to
> account for setup block") added headroom to the PE image to account for
> the setup block, which wasn't used for the decompression buffer.
>
> Now that we decompress from the start of the image, this is no longer
> required.
>
> Add a check to make sure that the head section of the compressed kernel
> won't overwrite itself while relocating. This is only for
> future-proofing as with current limits on the setup and the actual size
> of the head section, this can never happen.
>
> Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>

To make clear, the kernel (head_32.s and head_64.s) still relocates
itself to the end of the buffer and does in-place decompression. So this
is just to make init sz smaller.


> ---
> arch/x86/boot/tools/build.c | 28 ++++++++++++++++++++++++++--
> 1 file changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
> index 90d403dfec80..3d03ad753ed5 100644
> --- a/arch/x86/boot/tools/build.c
> +++ b/arch/x86/boot/tools/build.c
> @@ -65,6 +65,8 @@ unsigned long efi_pe_entry;
> unsigned long efi32_pe_entry;
> unsigned long kernel_info;
> unsigned long startup_64;
> +unsigned long _ehead;
> +unsigned long _end;
>
> /*----------------------------------------------------------------------*/
>
> @@ -232,7 +234,7 @@ static void update_pecoff_text(unsigned int text_start, unsigned int file_sz,
> {
> unsigned int pe_header;
> unsigned int text_sz = file_sz - text_start;
> - unsigned int bss_sz = init_sz + text_start - file_sz;
> + unsigned int bss_sz = init_sz - file_sz;
>
> pe_header = get_unaligned_le32(&buf[0x3c]);
>
> @@ -259,7 +261,7 @@ static void update_pecoff_text(unsigned int text_start, unsigned int file_sz,
> put_unaligned_le32(file_sz - 512 + bss_sz, &buf[pe_header + 0x1c]);
>
> /* Size of image */
> - put_unaligned_le32(init_sz + text_start, &buf[pe_header + 0x50]);
> + put_unaligned_le32(init_sz, &buf[pe_header + 0x50]);
>
> /*
> * Address of entry point for PE/COFF executable
> @@ -360,6 +362,8 @@ static void parse_zoffset(char *fname)
> PARSE_ZOFS(p, efi32_pe_entry);
> PARSE_ZOFS(p, kernel_info);
> PARSE_ZOFS(p, startup_64);
> + PARSE_ZOFS(p, _ehead);
> + PARSE_ZOFS(p, _end);
>
> p = strchr(p, '\n');
> while (p && (*p == '\r' || *p == '\n'))
> @@ -444,6 +448,26 @@ int main(int argc, char ** argv)
> put_unaligned_le32(sys_size, &buf[0x1f4]);
>
> init_sz = get_unaligned_le32(&buf[0x260]);
> +#ifdef CONFIG_EFI_STUB
> + /*
> + * The decompression buffer will start at ImageBase. When relocating
> + * the compressed kernel to its end, we must ensure that the head
> + * section does not get overwritten. The head section occupies
> + * [i, i + _ehead), and the destination is [init_sz - _end, init_sz).
> + *
> + * At present these should never overlap, because i is at most 32k
> + * because of SETUP_SECT_MAX, _ehead is less than 1k, and the
> + * calculation of INIT_SIZE in boot/header.S ensures that
> + * init_sz - _end is at least 64k.
> + *
> + * For future-proofing, increase init_sz if necessary.
> + */
> +
> + if (init_sz - _end < i + _ehead) {
> + init_sz = (i + _ehead + _end + 4095) & ~4095;
> + put_unaligned_le32(init_sz, &buf[0x260]);
> + }
> +#endif
> update_pecoff_text(setup_sectors * 512, i + (sys_size * 16), init_sz);
>
> efi_stub_entry_update();

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