From: Ard Biesheuvel <ardb+git@google.com>
To: linux-kernel@vger.kernel.org
Cc: x86@kernel.org, Ard Biesheuvel <ardb@kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
Eric Biederman <ebiederm@xmission.com>,
kexec@lists.infradead.org, Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Kees Cook <keescook@chromium.org>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>,
Masahiro Yamada <masahiroy@kernel.org>
Subject: [RFC PATCH 6/9] kexec: Add support for fully linked purgatory executables
Date: Wed, 24 Apr 2024 17:53:16 +0200 [thread overview]
Message-ID: <20240424155309.1719454-17-ardb+git@google.com> (raw)
In-Reply-To: <20240424155309.1719454-11-ardb+git@google.com>
From: Ard Biesheuvel <ardb@kernel.org>
The purgatory ELF object is typically a partially linked object, which
puts the burden on the kexec loader to lay out the executable in memory,
and this involves (among other things) deciding the placement of the
sections in memory, and fixing up all relocations (relative and absolute
ones)
All of this can be greatly simplified by using a fully linked PIE ELF
executable instead, constructed in a way that removes the need for any
relocation processing or layout and allocation of individual sections.
By gathering all allocatable sections into a single PT_LOAD segment, and
relying on RIP-relative references, all relocations will be applied by
the linker, and the segment simply needs to be copied into memory.
So add a linker script and some minimal handling in generic code, which
can be used by architectures to opt into this approach. This will be
wired up for x86 in a subsequent patch.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
include/asm-generic/purgatory.lds | 34 ++++++++++
kernel/kexec_file.c | 68 +++++++++++++++++++-
2 files changed, 101 insertions(+), 1 deletion(-)
diff --git a/include/asm-generic/purgatory.lds b/include/asm-generic/purgatory.lds
new file mode 100644
index 000000000000..260c457f7608
--- /dev/null
+++ b/include/asm-generic/purgatory.lds
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+PHDRS
+{
+ text PT_LOAD FLAGS(7) FILEHDR PHDRS;
+}
+
+SECTIONS
+{
+ . = SIZEOF_HEADERS;
+
+ .text : {
+ *(.text .rodata* .kexec-purgatory .data*)
+ } :text
+
+ .bss : {
+ *(.bss .dynbss)
+ } :text
+
+ .rela.dyn : {
+ *(.rela.*)
+ }
+
+ .symtab 0 : { *(.symtab) }
+ .strtab 0 : { *(.strtab) }
+ .shstrtab 0 : { *(.shstrtab) }
+
+ /DISCARD/ : {
+ *(.interp .modinfo .dynsym .dynstr .hash .gnu.* .dynamic .comment)
+ *(.got .plt .got.plt .plt.got .note.* .eh_frame .sframe)
+ }
+}
+
+ASSERT(SIZEOF(.rela.dyn) == 0, "Absolute relocations detected");
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index bef2f6f2571b..6379f8dfc29f 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -1010,6 +1010,62 @@ static int kexec_apply_relocations(struct kimage *image)
return 0;
}
+/*
+ * kexec_load_purgatory_pie - Load the position independent purgatory object.
+ * @pi: Purgatory info struct.
+ * @kbuf: Memory parameters to use.
+ *
+ * Load a purgatory PIE executable. This is a fully linked executable
+ * consisting of a single PT_LOAD segment that does not require any relocation
+ * processing.
+ *
+ * Return: 0 on success, negative errno on error.
+ */
+static int kexec_load_purgatory_pie(struct purgatory_info *pi,
+ struct kexec_buf *kbuf)
+{
+ const Elf_Phdr *phdr = (void *)pi->ehdr + pi->ehdr->e_phoff;
+ int ret;
+
+ if (pi->ehdr->e_phnum != 1)
+ return -EINVAL;
+
+ kbuf->bufsz = phdr->p_filesz;
+ kbuf->memsz = phdr->p_memsz;
+ kbuf->buf_align = phdr->p_align;
+
+ kbuf->buffer = vzalloc(kbuf->bufsz);
+ if (!kbuf->buffer)
+ return -ENOMEM;
+
+ ret = kexec_add_buffer(kbuf);
+ if (ret)
+ goto out_free_kbuf;
+
+ kbuf->image->start = kbuf->mem + pi->ehdr->e_entry;
+
+ pi->sechdrs = vcalloc(pi->ehdr->e_shnum, pi->ehdr->e_shentsize);
+ if (!pi->sechdrs)
+ goto out_free_kbuf;
+
+ pi->purgatory_buf = memcpy(kbuf->buffer,
+ (void *)pi->ehdr + phdr->p_offset,
+ kbuf->bufsz);
+
+ memcpy(pi->sechdrs, (void *)pi->ehdr + pi->ehdr->e_shoff,
+ pi->ehdr->e_shnum * pi->ehdr->e_shentsize);
+
+ for (int i = 0; i < pi->ehdr->e_shnum; i++)
+ if (pi->sechdrs[i].sh_flags & SHF_ALLOC)
+ pi->sechdrs[i].sh_addr += kbuf->mem;
+
+ return 0;
+
+out_free_kbuf:
+ vfree(kbuf->buffer);
+ return ret;
+}
+
/*
* kexec_load_purgatory - Load and relocate the purgatory object.
* @image: Image to add the purgatory to.
@@ -1031,6 +1087,9 @@ int kexec_load_purgatory(struct kimage *image, struct kexec_buf *kbuf)
pi->ehdr = (const Elf_Ehdr *)kexec_purgatory;
+ if (pi->ehdr->e_type != ET_REL)
+ return kexec_load_purgatory_pie(pi, kbuf);
+
ret = kexec_purgatory_setup_kbuf(pi, kbuf);
if (ret)
return ret;
@@ -1087,7 +1146,8 @@ static const Elf_Sym *kexec_purgatory_find_symbol(struct purgatory_info *pi,
/* Go through symbols for a match */
for (k = 0; k < sechdrs[i].sh_size/sizeof(Elf_Sym); k++) {
- if (ELF_ST_BIND(syms[k].st_info) != STB_GLOBAL)
+ if (pi->ehdr->e_type == ET_REL &&
+ ELF_ST_BIND(syms[k].st_info) != STB_GLOBAL)
continue;
if (strcmp(strtab + syms[k].st_name, name) != 0)
@@ -1159,6 +1219,12 @@ int kexec_purgatory_get_set_symbol(struct kimage *image, const char *name,
sym_buf = (char *)pi->purgatory_buf + sec->sh_offset + sym->st_value;
+ if (pi->ehdr->e_type != ET_REL) {
+ const Elf_Shdr *shdr = (void *)pi->ehdr + pi->ehdr->e_shoff;
+
+ sym_buf -= shdr[sym->st_shndx].sh_addr;
+ }
+
if (get_value)
memcpy((void *)buf, sym_buf, size);
else
--
2.44.0.769.g3c40516874-goog
next prev parent reply other threads:[~2024-04-24 15:53 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-24 15:53 [RFC PATCH 0/9] kexec x86 purgatory cleanup Ard Biesheuvel
2024-04-24 15:53 ` [RFC PATCH 1/9] x86/purgatory: Drop function entry padding from purgatory Ard Biesheuvel
2024-04-24 15:53 ` [RFC PATCH 2/9] x86/purgatory: Simplify stack handling Ard Biesheuvel
2024-04-24 18:26 ` Nathan Chancellor
2024-04-26 21:32 ` Justin Stitt
2024-04-26 21:53 ` Nathan Chancellor
2024-04-26 22:01 ` Justin Stitt
2024-04-24 15:53 ` [RFC PATCH 3/9] x86/purgatory: Drop pointless GDT switch Ard Biesheuvel
2024-04-24 15:53 ` [RFC PATCH 4/9] x86/purgatory: Avoid absolute reference to GDT Ard Biesheuvel
2024-04-24 17:38 ` Brian Gerst
2024-04-24 17:53 ` Ard Biesheuvel
2024-04-24 19:00 ` Brian Gerst
2024-04-24 15:53 ` [RFC PATCH 5/9] x86/purgatory: Simplify GDT and drop data segment Ard Biesheuvel
2024-04-24 15:53 ` Ard Biesheuvel [this message]
2024-04-24 15:53 ` [RFC PATCH 7/9] x86/purgatory: Use fully linked PIE ELF executable Ard Biesheuvel
2024-04-24 15:53 ` [RFC PATCH 8/9] x86/purgatory: Simplify references to regs array Ard Biesheuvel
2024-04-24 15:53 ` [RFC PATCH 9/9] kexec: Drop support for partially linked purgatory executables Ard Biesheuvel
2024-04-24 20:04 ` [RFC PATCH 0/9] kexec x86 purgatory cleanup Eric W. Biederman
2024-04-24 20:52 ` Ard Biesheuvel
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