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kexec: derive purgatory entry from symbol

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kexec_load_purgatory() derives image->start by locating e_entry inside an
SHF_EXECINSTR section.  If the purgatory object contains multiple
executable sections with overlapping sh_addr, the entrypoint check can
match more than once and trigger a WARN.

Derive the entry section from the purgatory_start symbol when present and
compute image->start from its final placement.  Keep the existing e_entry
fallback for purgatories that do not expose the symbol.

WARNING: kernel/kexec_file.c:1009 at kexec_load_purgatory+0x395/0x3c0, CPU#10: kexec/1784
Call Trace:
 <TASK>
 bzImage64_load+0x133/0xa00
 __do_sys_kexec_file_load+0x2b3/0x5c0
 do_syscall_64+0x81/0x610
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

[me@linux.beauty: move helper to avoid forward declaration, per Baoquan]
  Link: https://lkml.kernel.org/r/20260128043511.316860-1-me@linux.beauty
Link: https://lkml.kernel.org/r/20260120124005.148381-1-me@linux.beauty
Fixes: 8652d44f46 ("kexec: support purgatories with .text.hot sections")
Signed-off-by: Li Chen <me@linux.beauty>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Alexander Graf <graf@amazon.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Li Chen <me@linux.beauty>
Cc: Philipp Rudo <prudo@redhat.com>
Cc: Ricardo Ribalda Delgado <ribalda@chromium.org>
Cc: Ross Zwisler <zwisler@google.com>
Cc: Sourabh Jain <sourabhjain@linux.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Li Chen 2026-01-20 20:40:04 +08:00 • committed by Andrew Morton
parent 5138c936c2
commit 480e1d5c64
1 changed files with 74 additions and 57 deletions
Download patch file Download diff file Expand all files Collapse all files

131
kernel/kexec_file.c
View file

@ -882,6 +882,60 @@ out_free_sha_regions:
}
#ifdef CONFIG_ARCH_SUPPORTS_KEXEC_PURGATORY
/*
* kexec_purgatory_find_symbol - find a symbol in the purgatory
* @pi: Purgatory to search in.
* @name: Name of the symbol.
*
* Return: pointer to symbol in read-only symtab on success, NULL on error.
*/
static const Elf_Sym *kexec_purgatory_find_symbol(struct purgatory_info *pi,
const char *name)
{
const Elf_Shdr *sechdrs;
const Elf_Ehdr *ehdr;
const Elf_Sym *syms;
const char *strtab;
int i, k;
if (!pi->ehdr)
return NULL;
ehdr = pi->ehdr;
sechdrs = (void *)ehdr + ehdr->e_shoff;
for (i = 0; i < ehdr->e_shnum; i++) {
if (sechdrs[i].sh_type != SHT_SYMTAB)
continue;
if (sechdrs[i].sh_link >= ehdr->e_shnum)
/* Invalid strtab section number */
continue;
strtab = (void *)ehdr + sechdrs[sechdrs[i].sh_link].sh_offset;
syms = (void *)ehdr + sechdrs[i].sh_offset;
/* 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)
continue;
if (strcmp(strtab + syms[k].st_name, name) != 0)
continue;
if (syms[k].st_shndx == SHN_UNDEF ||
syms[k].st_shndx >= ehdr->e_shnum) {
pr_debug("Symbol: %s has bad section index %d.\n",
name, syms[k].st_shndx);
return NULL;
}
/* Found the symbol we are looking for */
return &syms[k];
}
}
return NULL;
}
/*
* kexec_purgatory_setup_kbuf - prepare buffer to load purgatory.
* @pi: Purgatory to be loaded.
@ -960,6 +1014,10 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
unsigned long offset;
size_t sechdrs_size;
Elf_Shdr *sechdrs;
const Elf_Sym *entry_sym;
u16 entry_shndx = 0;
unsigned long entry_off = 0;
bool start_fixed = false;
int i;
/*
@ -977,6 +1035,12 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
bss_addr = kbuf->mem + kbuf->bufsz;
kbuf->image->start = pi->ehdr->e_entry;
entry_sym = kexec_purgatory_find_symbol(pi, "purgatory_start");
if (entry_sym) {
entry_shndx = entry_sym->st_shndx;
entry_off = entry_sym->st_value;
}
for (i = 0; i < pi->ehdr->e_shnum; i++) {
unsigned long align;
void *src, *dst;
@ -994,6 +1058,13 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
offset = ALIGN(offset, align);
if (!start_fixed && entry_sym && i == entry_shndx &&
(sechdrs[i].sh_flags & SHF_EXECINSTR) &&
entry_off < sechdrs[i].sh_size) {
kbuf->image->start = kbuf->mem + offset + entry_off;
start_fixed = true;
}
/*
* Check if the segment contains the entry point, if so,
* calculate the value of image->start based on it.
@ -1004,13 +1075,14 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
* is not set to the initial value, and warn the user so they
* have a chance to fix their purgatory's linker script.
*/
if (sechdrs[i].sh_flags & SHF_EXECINSTR &&
if (!start_fixed && sechdrs[i].sh_flags & SHF_EXECINSTR &&
pi->ehdr->e_entry >= sechdrs[i].sh_addr &&
pi->ehdr->e_entry < (sechdrs[i].sh_addr
+ sechdrs[i].sh_size) &&
!WARN_ON(kbuf->image->start != pi->ehdr->e_entry)) {
kbuf->image->start == pi->ehdr->e_entry) {
kbuf->image->start -= sechdrs[i].sh_addr;
kbuf->image->start += kbuf->mem + offset;
start_fixed = true;
}
src = (void *)pi->ehdr + sechdrs[i].sh_offset;
@ -1128,61 +1200,6 @@ out_free_kbuf:
return ret;
}
/*
* kexec_purgatory_find_symbol - find a symbol in the purgatory
* @pi: Purgatory to search in.
* @name: Name of the symbol.
*
* Return: pointer to symbol in read-only symtab on success, NULL on error.
*/
static const Elf_Sym *kexec_purgatory_find_symbol(struct purgatory_info *pi,
const char *name)
{
const Elf_Shdr *sechdrs;
const Elf_Ehdr *ehdr;
const Elf_Sym *syms;
const char *strtab;
int i, k;
if (!pi->ehdr)
return NULL;
ehdr = pi->ehdr;
sechdrs = (void *)ehdr + ehdr->e_shoff;
for (i = 0; i < ehdr->e_shnum; i++) {
if (sechdrs[i].sh_type != SHT_SYMTAB)
continue;
if (sechdrs[i].sh_link >= ehdr->e_shnum)
/* Invalid strtab section number */
continue;
strtab = (void *)ehdr + sechdrs[sechdrs[i].sh_link].sh_offset;
syms = (void *)ehdr + sechdrs[i].sh_offset;
/* 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)
continue;
if (strcmp(strtab + syms[k].st_name, name) != 0)
continue;
if (syms[k].st_shndx == SHN_UNDEF ||
syms[k].st_shndx >= ehdr->e_shnum) {
pr_debug("Symbol: %s has bad section index %d.\n",
name, syms[k].st_shndx);
return NULL;
}
/* Found the symbol we are looking for */
return &syms[k];
}
}
return NULL;
}
void *kexec_purgatory_get_symbol_addr(struct kimage *image, const char *name)
{
struct purgatory_info *pi = &image->purgatory_info;