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//===-- Implementation file of gnu_property_section -----------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "startup/linux/gnu_property_section.h"
#include "hdr/elf_proxy.h"
#include "hdr/link_macros.h"
#include "src/__support/CPP/string_view.h"
#include "src/__support/macros/config.h"
#include "src/string/memory_utils/utils.h"
namespace LIBC_NAMESPACE_DECL {
// The program property note is basically a note (Elf64_Nhdr) prepended with:
// * n_name[4]: should always be "GNU\0"
// * n_desc: an array of n_descsz bytes with program property entries
// Since we are casting a memory address into this struct, the layout needs to
// *exactly* match.
struct Elf64_ProgramPropertyNote {
Elf64_Nhdr nhdr;
unsigned char n_name[4];
unsigned char n_desc[0]; // the size of 'n_desc' depends on n_descsz and is
// not known statically.
};
// 32-bit variant for ProgramPropertyNote.
struct Elf32_ProgramPropertyNote {
Elf32_Nhdr nhdr;
unsigned char n_name[4];
unsigned char n_desc[0]; // the size of 'n_desc' depends on n_descsz and is
// not known statically.
};
// A program property consists of a type, the data size, followed by the actual
// data and potential padding (aligning it to 64bit).
// Since we are casting a memory address into this struct, the layout needs to
// *exactly* match (The padding is ommited since it doesn't have actual
// content).
// pr_data needs to be ElfW_Word aligned, therefore the whole struct needs to be
// aligned.
struct Elf64_ProgramProperty {
Elf64_Word pr_type;
Elf64_Word pr_datasz;
unsigned char pr_data[0];
};
// 32-bit variant for ProgramProperty.
struct Elf32_ProgramProperty {
Elf32_Word pr_type;
Elf32_Word pr_datasz;
unsigned char pr_data[0];
};
bool GnuPropertySection::parse(const ElfW(Phdr) * gnu_property_phdr,
const ElfW(Addr) base) {
if (!gnu_property_phdr)
return false;
const auto note_nhdr_size = gnu_property_phdr->p_memsz;
// Sanity check we are using the correct phdr and the memory size is large
// enough to fit the program property note.
if (gnu_property_phdr->p_type != PT_GNU_PROPERTY ||
note_nhdr_size < sizeof(ElfW(ProgramPropertyNote)))
return false;
const ElfW(ProgramPropertyNote) *note_nhdr =
reinterpret_cast<ElfW(ProgramPropertyNote) *>(base +
gnu_property_phdr->p_vaddr);
if (!note_nhdr)
return false;
const ElfW(Word) nhdr_desc_size = note_nhdr->nhdr.n_descsz;
// sizeof(*note_nhdr) does not include the size of n_desc,
// since it is not known at compile time.
// The size of it combined with n_descsz cannot exceed the total size of the
// program property note.
if ((sizeof(*note_nhdr) + nhdr_desc_size) > note_nhdr_size)
return false;
if (note_nhdr->nhdr.n_namesz != 4 ||
note_nhdr->nhdr.n_type != NT_GNU_PROPERTY_TYPE_0 ||
cpp::string_view(reinterpret_cast<const char *>(note_nhdr->n_name), 4) !=
cpp::string_view("GNU", 4))
return false;
// program property note is valid, we can parse the program property array.
ElfW(Word) offset = 0;
// Process properties until we can no longer even fit the statically known
// size of ProgramProperty.
while (offset + sizeof(ElfW(ProgramProperty)) <= nhdr_desc_size) {
const ElfW(ProgramProperty) *property =
reinterpret_cast<const ElfW(ProgramProperty) *>(
¬e_nhdr->n_desc[offset]);
// Sanity check that property is correctly aligned.
if (distance_to_align_up<sizeof(ElfW(Word))>(property) > 0)
return false;
const ElfW(Xword) property_size = sizeof(*property) + property->pr_datasz;
// Also check that pr_data does not reach out of bounds.
if ((offset + property_size) > nhdr_desc_size)
return false;
switch (property->pr_type) {
#ifdef LIBC_TARGET_ARCH_IS_X86_64
case GNU_PROPERTY_X86_FEATURE_1_AND: {
// PR_DATASZ should always be 4 bytes, for both 32bit and 64bit.
if (property->pr_datasz != 4)
return false;
const uint32_t feature_bitmap =
*reinterpret_cast<const uint32_t *>(&property->pr_data[0]);
features_.shstk_supported =
(feature_bitmap & GNU_PROPERTY_X86_FEATURE_1_SHSTK) != 0;
break;
}
#endif
default:
break;
}
offset += static_cast<ElfW(Word)>(property_size);
}
return true;
}
} // namespace LIBC_NAMESPACE_DECL