[PATCH 6.18 644/752] kexec: derive purgatory entry from symbol

Sasha Levin
2026-02-28T17:57:39Z

From: Li Chen <me@linux.beauty>

[ Upstream commit 480e1d5c64bb14441f79f2eb9421d5e26f91ea3d ]

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: 8652d44f466a ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/kexec_file.c | 131 +++++++++++++++++++++++++-------------------
1 file changed, 74 insertions(+), 57 deletions(-)

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index eb62a97942428..2bfbb2d144e69 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -882,6 +882,60 @@ static int kexec_calculate_store_digests(struct kimage *image)
}

#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 @@ int kexec_load_purgatory(struct kimage *image, struct kexec_buf *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;
--
2.51.0