From: Fangrui Song <i@maskray.me>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: binutils@sourceware.org
Subject: Re: [PATCH] elf: Remove the 1-page gap before the RELRO segment
Date: Mon, 10 Jan 2022 21:26:09 -0800 [thread overview]
Message-ID: <20220111052609.neg3brvkhyqzy4vd@gmail.com> (raw)
In-Reply-To: <20220111021241.1937265-1-hjl.tools@gmail.com>
On 2022-01-10, H.J. Lu via Binutils wrote:
>The existing RELRO scheme may leave a 1-page gap before the RELRO segment
>and align the end of the RELRO segment to the page size:
>
> [18] .eh_frame PROGBITS 408fa0 008fa0 005e80 00 A 0 0 8
> [19] .init_array INIT_ARRAY 410de0 00fde0 000008 08 WA 0 0 8
> [20] .fini_array FINI_ARRAY 410de8 00fde8 000008 08 WA 0 0 8
> [21] .dynamic DYNAMIC 410df0 00fdf0 000200 10 WA 7 0 8
> [22] .got PROGBITS 410ff0 00fff0 000010 08 WA 0 0 8
> [23] .got.plt PROGBITS 411000 010000 000048 08 WA 0 0 8
>
>Instead, we can remove the 1-page gap if the maximum page size >= the
>maximum section alignment:
>
> [18] .eh_frame PROGBITS 408fa0 008fa0 005e80 00 A 0 0 8
> [19] .init_array INIT_ARRAY 40fde0 00fde0 000008 08 WA 0 0 8
> [20] .fini_array FINI_ARRAY 40fde8 00fde8 000008 08 WA 0 0 8
> [21] .dynamic DYNAMIC 40fdf0 00fdf0 000200 10 WA 7 0 8
> [22] .got PROGBITS 40fff0 00fff0 000010 08 WA 0 0 8
> [23] .got.plt PROGBITS 410000 010000 000048 08 WA 0 0 8
>
>Because the end of the RELRO segment is always aligned to the page size
>and may not be moved, the RELRO segment size may be increased:
>
> [ 3] .dynstr STRTAB 000148 000148 000001 00 A 0 0 1
> [ 4] .eh_frame PROGBITS 000150 000150 000000 00 A 0 0 8
> [ 5] .init_array INIT_ARRAY 200150 000150 000010 08 WA 0 0 1
> [ 6] .fini_array FINI_ARRAY 200160 000160 000010 08 WA 0 0 1
> [ 7] .jcr PROGBITS 200170 000170 000008 00 WA 0 0 1
> [ 8] .data.rel.ro PROGBITS 200180 000180 000020 00 WA 0 0 16
> [ 9] .dynamic DYNAMIC 2001a0 0001a0 0001c0 10 WA 3 0 8
> [10] .got PROGBITS 200360 000360 0002a8 00 WA 0 0 8
> [11] .bss NOBITS 201000 000608 000840 00 WA 0 0 1
>
>vs the old section layout:
>
> [ 3] .dynstr STRTAB 000148 000148 000001 00 A 0 0 1
> [ 4] .eh_frame PROGBITS 000150 000150 000000 00 A 0 0 8
> [ 5] .init_array INIT_ARRAY 200b48 000b48 000010 08 WA 0 0 1
> [ 6] .fini_array FINI_ARRAY 200b58 000b58 000010 08 WA 0 0 1
> [ 7] .jcr PROGBITS 200b68 000b68 000008 00 WA 0 0 1
> [ 8] .data.rel.ro PROGBITS 200b70 000b70 000020 00 WA 0 0 16
> [ 9] .dynamic DYNAMIC 200b90 000b90 0001c0 10 WA 3 0 8
> [10] .got PROGBITS 200d50 000d50 0002a8 00 WA 0 0 8
> [11] .bss NOBITS 201000 000ff8 000840 00 WA 0 0 1
>
>But there is no 1-page gap.
> [...}
If you want to avoid a max-page-size alignment (at the end of PT_GNU_RELRO), you may adopt ld.lld's design
I implemented:
LOAD 0x000000 0x0000000000200000 0x0000000000200000 0xcaac4c 0xcaac4c R 0x1000
LOAD 0xcaac50 0x0000000000eabc50 0x0000000000eabc50 0x208a0c0 0x208a0c0 R E 0x1000
LOAD 0x2d34d10 0x0000000002f36d10 0x0000000002f36d10 0x1777e8 0x1777e8 RW 0x1000 match
LOAD 0x2eac500 0x00000000030af500 0x00000000030af500 0x008038 0x064664 RW 0x1000
TLS 0x2d34d10 0x0000000002f35d10 0x0000000002f35d10 0x000000 0x000018 R 0x8
DYNAMIC 0x2ea5570 0x00000000030a7570 0x00000000030a7570 0x000240 0x000240 RW 0x8
GNU_RELRO 0x2d34d10 0x0000000002f36d10 0x0000000002f36d10 0x1777e8 0x1782f0 R 0x1 match
GNU_EH_FRAME 0x89ce34 0x0000000000a9ce34 0x0000000000a9ce34 0x08586c 0x08586c R 0x4
GNU_STACK 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW 0
NOTE 0x0002fc 0x00000000002002fc 0x00000000002002fc 0x000020 0x000020 R 0x4
The idea is to have 2 RW PT_LOAD with one exactly matching PT_GNU_RELRO.
next prev parent reply other threads:[~2022-01-11 5:26 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-11 2:12 H.J. Lu
2022-01-11 5:26 ` Fangrui Song [this message]
2022-01-13 12:44 ` Nick Clifton
2022-01-13 12:52 ` Alan Modra
2022-01-13 13:19 ` H.J. Lu
2022-01-14 8:12 ` Alan Modra
2022-01-14 9:37 ` Fangrui Song
2022-01-14 14:58 ` H.J. Lu
2022-01-14 21:55 ` [PATCH] ld: Rewrite lang_size_relro_segment_1 H.J. Lu
2022-01-17 4:08 ` Alan Modra
2022-01-18 4:16 ` [PATCH v2] " H.J. Lu
[not found] ` <CAMe9rOpdkYZDigz8r_oPbweLnaCJUjx3-L-v-vp-70c0MGOHQw@mail.gmail.com>
2022-01-24 16:24 ` Fwd: " Nick Clifton
2022-01-24 21:17 ` [PATCH v3] " H.J. Lu
2022-01-25 15:05 ` [PATCH v4] " H.J. Lu
2022-01-26 10:55 ` Nick Clifton
2022-01-27 0:48 ` Alan Modra
2022-01-27 2:10 ` H.J. Lu
2022-01-29 1:01 ` Alan Modra
2022-01-29 9:06 ` Fangrui Song
2022-01-29 16:45 ` H.J. Lu
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