[PATCH 01/19] x86/elf: Check in_x32_syscall() in compat_arch_setup_additional_pages()

[Dmitry Safonov <dima@arista.com>]

Partly revert commit 3316ec8ccd34 ("x86/elf: Use e_machine to check for
x32/ia32 in setup_additional_pages()") and commit 9a29a671902c ("elf:
Expose ELF header on arch_setup_additional_pages()".
Both patches did a good thing: removed usage of TIF_X32, but with
a price of additional macros ARCH_SETUP_ADDITIONAL_PAGES() and ifdeffs.

Instead, use in_x32_syscall() - the first thing load_elf_binary() does
after parsing and checking new ELF binary. It's done that early which
also allows to use it in mmap() code straight away, which needs it
to know which mmap_base to use (see arch_pick_mmap_layout()).
Add comments that describe how it works.

Cc: x86@kernel.org
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
 arch/x86/entry/vdso/vma.c     |  4 ++--
 arch/x86/include/asm/compat.h |  6 ++++++
 arch/x86/include/asm/elf.h    |  6 ++----
 fs/binfmt_elf.c               | 10 +++++++---
 fs/compat_binfmt_elf.c        | 11 +++--------
 include/linux/elf.h           |  5 -----
 6 files changed, 20 insertions(+), 22 deletions(-)

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 44de75b21fab..4eea508e9b10 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -396,10 +396,10 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 
 #ifdef CONFIG_COMPAT
 int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
-				       int uses_interp, bool x32)
+				       int uses_interp)
 {
 #ifdef CONFIG_X86_X32_ABI
-	if (x32) {
+	if (in_x32_syscall()) {
 		if (!vdso64_enabled)
 			return 0;
 		return map_vdso_randomized(&vdso_image_x32);
diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
index f145e3326c6d..4489bd60640b 100644
--- a/arch/x86/include/asm/compat.h
+++ b/arch/x86/include/asm/compat.h
@@ -197,6 +197,12 @@ static inline bool in_x32_syscall(void)
 	return false;
 }
 
+/*
+ * Valid all time on the context of process that performs a syscall.
+ * Just born process has __X32_SYSCALL_BIT or TS_COMPAT set very
+ * early in load_binary() on setting personality and flags.
+ * See also set_personality_ia32().
+ */
 static inline bool in_32bit_syscall(void)
 {
 	return in_ia32_syscall() || in_x32_syscall();
diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 44a9b9940535..109697a19eb1 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -383,10 +383,8 @@ struct linux_binprm;
 extern int arch_setup_additional_pages(struct linux_binprm *bprm,
 				       int uses_interp);
 extern int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
-					      int uses_interp, bool x32);
-#define COMPAT_ARCH_SETUP_ADDITIONAL_PAGES(bprm, ex, interpreter)	\
-	compat_arch_setup_additional_pages(bprm, interpreter,		\
-					   (ex->e_machine == EM_X86_64))
+					      int uses_interp);
+#define compat_arch_setup_additional_pages compat_arch_setup_additional_pages
 
 /* Do not change the values. See get_align_mask() */
 enum align_flags {
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index ac0b5fc30ea6..3de72c0e0406 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -999,8 +999,12 @@ static int load_elf_binary(struct linux_binprm *bprm)
 	if (retval)
 		goto out_free_dentry;
 
-	/* Do this immediately, since STACK_TOP as used in setup_arg_pages
-	   may depend on the personality.  */
+	/*
+	 * Do this immediately, since STACK_TOP as used in setup_arg_pages
+	 * may depend on the personality. At this moment we start
+	 * pretending that we are in a context of compat syscall for
+	 * compatible applications on x86, in_compat_syscall() starts working.
+	 */
 	SET_PERSONALITY2(*elf_ex, &arch_state);
 	if (elf_read_implies_exec(*elf_ex, executable_stack))
 		current->personality |= READ_IMPLIES_EXEC;
@@ -1246,7 +1250,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
 	set_binfmt(&elf_format);
 
 #ifdef ARCH_HAS_SETUP_ADDITIONAL_PAGES
-	retval = ARCH_SETUP_ADDITIONAL_PAGES(bprm, elf_ex, !!interpreter);
+	retval = arch_setup_additional_pages(bprm, !!interpreter);
 	if (retval < 0)
 		goto out;
 #endif /* ARCH_HAS_SETUP_ADDITIONAL_PAGES */
diff --git a/fs/compat_binfmt_elf.c b/fs/compat_binfmt_elf.c
index 2c557229696a..12b991368f0a 100644
--- a/fs/compat_binfmt_elf.c
+++ b/fs/compat_binfmt_elf.c
@@ -115,16 +115,11 @@
 #define START_THREAD		COMPAT_START_THREAD
 #endif
 
-#ifdef compat_arch_setup_additional_pages
-#define COMPAT_ARCH_SETUP_ADDITIONAL_PAGES(bprm, ex, interpreter) \
-	compat_arch_setup_additional_pages(bprm, interpreter)
-#endif
-
-#ifdef	COMPAT_ARCH_SETUP_ADDITIONAL_PAGES
+#ifdef	compat_arch_setup_additional_pages
 #undef	ARCH_HAS_SETUP_ADDITIONAL_PAGES
 #define ARCH_HAS_SETUP_ADDITIONAL_PAGES 1
-#undef	ARCH_SETUP_ADDITIONAL_PAGES
-#define	ARCH_SETUP_ADDITIONAL_PAGES COMPAT_ARCH_SETUP_ADDITIONAL_PAGES
+#undef	arch_setup_additional_pages
+#define	arch_setup_additional_pages compat_arch_setup_additional_pages
 #endif
 
 #ifdef	compat_elf_read_implies_exec
diff --git a/include/linux/elf.h b/include/linux/elf.h
index c9a46c4e183b..6dbcfe7a3fd7 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -27,11 +27,6 @@
 	start_thread(regs, elf_entry, start_stack)
 #endif
 
-#if defined(ARCH_HAS_SETUP_ADDITIONAL_PAGES) && !defined(ARCH_SETUP_ADDITIONAL_PAGES)
-#define ARCH_SETUP_ADDITIONAL_PAGES(bprm, ex, interpreter) \
-	arch_setup_additional_pages(bprm, interpreter)
-#endif
-
 #define ELF32_GNU_PROPERTY_ALIGN	4
 #define ELF64_GNU_PROPERTY_ALIGN	8
 
-- 
2.28.0