| 1 | |
| 2 | |
| 3 | * Static branch in a patched function. The jump table entry is written out by
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| 4 | * hand, mirroring JUMP_TABLE_ENTRY(), so the fixture builds without kernel
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| 5 | * headers. The key is an STT_OBJECT; anything else is ignored by
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| 6 | * validate_special_section_klp_reloc().
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| 7 | *
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| 8 | * MODNAME selects whether the key is taken to belong to vmlinux or a module.
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| 9 | *
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| 10 | * NEW_KEY puts the whole static branch behind PATCHED, so the patch introduces
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| 11 | * one where the original had none -- a different question from patching code
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| 12 | * that already has a key, because the __jump_table entry itself is new.
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| 13 | *
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| 14 | * KEY_NAME renames the key. Two names are special to
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| 15 | * validate_special_section_klp_reloc(): a __tracepoint_* key and the
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| 16 | * __UNIQUE_ID_ddebug_* one pr_debug() generates are both unsupported in a
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| 17 | * module, but are disabled with a warning rather than rejected, because the
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| 18 | * kernel is full of them and refusing outright would make ordinary functions
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| 19 | * unpatchable.
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| 20 | *
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| 21 | * STATIC_KEY makes the key file-local. That changes the shape of the
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| 22 | * relocation rather than the meaning of the code: a reference to a static lands
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| 23 | * on the section symbol plus an addend, so the key has to be resolved from the
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| 24 | * section before it can be recognised as a key at all.
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| 25 |
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| 26 |
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| 27 | #ifndef MODNAME
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| 28 | #define MODNAME "vmlinux"
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| 29 | #endif
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| 30 |
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| 31 | #ifndef KEY_NAME
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| 32 | #define KEY_NAME klp_test_key
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| 33 | #endif
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| 34 |
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| 35 | static const char __modinfo[]
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| 36 | __attribute__((section(".modinfo"), used, aligned(1))) = "\0name=" MODNAME;
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| 37 |
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| 38 | #ifdef STATIC_KEY
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| 39 | static long KEY_NAME;
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| 40 | #else
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| 41 | long KEY_NAME;
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| 42 | #endif
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| 43 |
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| 44 | int target(int x)
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| 45 | {
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| 46 | int r = x;
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| 47 |
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| 48 | #if defined(NEW_KEY) && !defined(PATCHED)
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| 49 |
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| 50 | return r + 1;
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| 51 | #else
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| 52 | asm goto(
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| 53 | "1: nop\n\t"
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| 54 | ".pushsection __jump_table, \"aw\"\n\t"
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| 55 | ".balign 8\n\t"
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| 56 | "912:\n\t"
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| 57 | ".pushsection .discard.annotate_data, \"M\", @progbits, 8\n\t"
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| 58 | ".long 912b - ., 1\n\t"
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| 59 | ".popsection\n\t"
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| 60 | ".long 1b - ., %l[l_yes] - .\n\t"
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| 61 | ".quad %c0 - .\n\t"
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| 62 | ".popsection\n\t"
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| 63 | : : "i" (&KEY_NAME) : : l_yes);
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| 64 |
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| 65 | r += 1;
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| 66 | goto out;
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| 67 | l_yes:
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| 68 | r += 2;
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| 69 | out:
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| 70 | #endif
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| 71 | #ifdef PATCHED
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| 72 | return r + 100;
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| 73 | #else
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| 74 | return r;
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| 75 | #endif
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| 76 | }
|