[PATCH RESEND] elf: add AT_ARGV and AT_ENVV auxiliary vector entries

[Alexandra Hájková]

Add AT_ARGV (52), which contains the address of the argv pointer
array on the initial process stack, and AT_ENVV (53), which contains
the address of the envp pointer array.

The motivation is to allow GDB to find argv and envp in core dumps
cleanly. Currently GDB locates them by scanning backwards through
stack memory from AT_EXECFN, which is fragile. With AT_ARGV and
AT_ENVV it can read the addresses directly from the core dump's
auxv note.

Signed-off-by: Alexandra Hájková <ahajkova@xxxxxxxxxx>
---
Resending after no response for 4 weeks.

 fs/binfmt_elf.c             | 9 ++++++++-
 include/linux/auxvec.h      | 2 +-
 include/uapi/linux/auxvec.h | 2 ++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 8e89cc5b2820..c2b3032adccb 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -182,6 +182,8 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
 	int ei_index;
 	const struct cred *cred = current_cred();
 	struct vm_area_struct *vma;
+	elf_addr_t *at_argv_val;
+	elf_addr_t *at_envv_val;
 
 	/*
 	 * In some cases (e.g. Hyper-Threading), we want to avoid L1
@@ -288,6 +290,10 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
 	NEW_AUX_ENT(AT_RSEQ_FEATURE_SIZE, offsetof(struct rseq, end));
 	NEW_AUX_ENT(AT_RSEQ_ALIGN, __alignof__(struct rseq));
 #endif
+	at_argv_val = elf_info + 1;
+	NEW_AUX_ENT(AT_ARGV, 0);
+	at_envv_val = elf_info + 1;
+	NEW_AUX_ENT(AT_ENVV, 0);
 #undef NEW_AUX_ENT
 	/* AT_NULL is zero; clear the rest too */
 	memset(elf_info, 0, (char *)mm->saved_auxv +
@@ -309,7 +315,8 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
 #else
 	sp = (elf_addr_t __user *)bprm->p;
 #endif
-
+	*at_argv_val = (unsigned long)(sp + sizeof(elf_addr_t));
+	*at_envv_val = (unsigned long)(sp + (argc + 2));
 
 	/*
 	 * Grow the stack manually; some architectures have a limit on how
diff --git a/include/linux/auxvec.h b/include/linux/auxvec.h
index 8bcb9b726262..7184de95b89d 100644
--- a/include/linux/auxvec.h
+++ b/include/linux/auxvec.h
@@ -4,6 +4,6 @@
 
 #include <uapi/linux/auxvec.h>
 
-#define AT_VECTOR_SIZE_BASE 24 /* NEW_AUX_ENT entries in auxiliary table */
+#define AT_VECTOR_SIZE_BASE 26 /* NEW_AUX_ENT entries in auxiliary table */
   /* number of "#define AT_.*" above, minus {AT_NULL, AT_IGNORE, AT_NOTELF} */
 #endif /* _LINUX_AUXVEC_H */
diff --git a/include/uapi/linux/auxvec.h b/include/uapi/linux/auxvec.h
index cc61cb9b3e9a..e7af32709aba 100644
--- a/include/uapi/linux/auxvec.h
+++ b/include/uapi/linux/auxvec.h
@@ -40,5 +40,7 @@
 #ifndef AT_MINSIGSTKSZ
 #define AT_MINSIGSTKSZ	51	/* minimal stack size for signal delivery */
 #endif
+#define AT_ARGV		52	/* address of argv[] */
+#define AT_ENVV		53	/* address of envp[] */
 
 #endif /* _UAPI_LINUX_AUXVEC_H */
-- 
2.52.0