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Message-ID: <aXnWMmyUMdbrqAiu@MiWiFi-R3L-srv>
Date: Wed, 28 Jan 2026 17:26:10 +0800
From: Baoquan He <bhe@...hat.com>
To: Li Chen <me@...ux.beauty>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Mimi Zohar <zohar@...ux.ibm.com>,
Tushar Sugandhi <tusharsu@...ux.microsoft.com>,
Eric Biggers <ebiggers@...nel.org>,
Alexander Graf <graf@...zon.com>,
Steven Chen <chenste@...ux.microsoft.com>,
Coiby Xu <coxu@...hat.com>,
Sourabh Jain <sourabhjain@...ux.ibm.com>,
Philipp Rudo <prudo@...hat.com>,
Ricardo Ribalda <ribalda@...omium.org>,
"Steven Rostedt (Google)" <rostedt@...dmis.org>,
Ross Zwisler <zwisler@...gle.com>, kexec@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] kexec: derive purgatory entry from symbol
On 01/28/26 at 12:35pm, Li Chen wrote:
> 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
>
> Fixes: 8652d44f466a ("kexec: support purgatories with .text.hot sections")
> Signed-off-by: Li Chen <me@...ux.beauty>
LGTM,
Acked-by: Baoquan He <bhe@...hat.com>
By the way, a warning need be 'Fixes' tag and back ported to stable
kernel?
Thanks
Baoquan
> ---
> clangelog:
> v2: move the helper body above kexec_purgatory_setup_sechdrs() in v2 to avoid
> the forward declaration, as suggested by Baoquan.
>
> 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 3f1d6c4e8ff2..e9550bfbd02e 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -880,6 +880,60 @@ 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.
> @@ -958,6 +1012,10 @@ 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;
>
> /*
> @@ -975,6 +1033,12 @@ 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;
> @@ -992,6 +1056,13 @@ 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.
> @@ -1002,13 +1073,14 @@ 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;
> @@ -1126,61 +1198,6 @@ 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;
> --
> 2.52.0
>
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