Commit 480e1d5c authored by Li Chen's avatar Li Chen Committed by Andrew Morton
Browse files

kexec: derive purgatory entry from symbol 

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: 8652d44f ("kexec: support purgatories with .text.hot sections")
Signed-off-by: default avatarLi Chen <me@linux.beauty>
Acked-by: default avatarBaoquan 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 5138c936

kernel/kexec_file.c

+74 −57
Original line number Diff line number Diff line
@@ -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;