Patch "x86/elf: Use e_machine to select start_thread for x32" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    x86/elf: Use e_machine to select start_thread for x32

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-elf-use-e_machine-to-select-start_thread-for-x32.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit b3fe0ecd86fb80ade5819a9271716fe1e04e9b1c
Author: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
Date:   Sat Oct 3 23:25:32 2020 -0400

    x86/elf: Use e_machine to select start_thread for x32
    
    [ Upstream commit 2424b14605c71a7187c14edd525044eb36bdea47 ]
    
    Since TIF_X32 is going away, avoid using it to find the ELF type in
    compat_start_thread.
    
    According to SysV AMD64 ABI Draft, an AMD64 ELF object using ILP32 must
    have ELFCLASS32 with (E_MACHINE == EM_X86_64), so use that ELF field to
    differentiate a x32 object from a IA32 object when executing start_thread()
    in compat mode.
    
    Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
    Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
    Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20201004032536.1229030-7-krisman@xxxxxxxxxxxxx
    Stable-dep-of: 7fea700e04bd ("zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with TIF_SIGPENDING")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index b9a5d488f1a5e..b7e3fa0dcd970 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -186,8 +186,9 @@ static inline void elf_common_init(struct thread_struct *t,
 #define	COMPAT_ELF_PLAT_INIT(regs, load_addr)		\
 	elf_common_init(&current->thread, regs, __USER_DS)
 
-void compat_start_thread(struct pt_regs *regs, u32 new_ip, u32 new_sp);
-#define compat_start_thread compat_start_thread
+void compat_start_thread(struct pt_regs *regs, u32 new_ip, u32 new_sp, bool x32);
+#define COMPAT_START_THREAD(ex, regs, new_ip, new_sp)	\
+	compat_start_thread(regs, new_ip, new_sp, ex->e_machine == EM_X86_64)
 
 void set_personality_ia32(bool);
 #define COMPAT_SET_PERSONALITY(ex)			\
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 1d8bc4736fb79..997d6556f4be8 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -511,11 +511,10 @@ start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
 EXPORT_SYMBOL_GPL(start_thread);
 
 #ifdef CONFIG_COMPAT
-void compat_start_thread(struct pt_regs *regs, u32 new_ip, u32 new_sp)
+void compat_start_thread(struct pt_regs *regs, u32 new_ip, u32 new_sp, bool x32)
 {
 	start_thread_common(regs, new_ip, new_sp,
-			    test_thread_flag(TIF_X32)
-			    ? __USER_CS : __USER32_CS,
+			    x32 ? __USER_CS : __USER32_CS,
 			    __USER_DS, __USER_DS);
 }
 #endif