Commit ff170cd0 authored by Gabriel Krisman Bertazi's avatar Gabriel Krisman Bertazi Committed by Thomas Gleixner
Browse files

x86/mm: Convert mmu context ia32_compat into a proper flags field 



The ia32_compat attribute is a weird thing.  It mirrors TIF_IA32 and
TIF_X32 and is used only in two very unrelated places: (1) to decide if
the vsyscall page is accessible (2) for uprobes to find whether the
patched instruction is 32 or 64 bit.

In preparation to remove the TIF flags, a new mechanism is required for
ia32_compat, but given its odd semantics, adding a real flags field which
configures these specific behaviours is the best option.

So, set_personality_x64() can ask for the vsyscall page, which is not
available in x32/ia32 and set_personality_ia32() can configure the uprobe
code as needed.

uprobe cannot rely on other methods like user_64bit_mode() to decide how
to patch, so it needs some specific flag like this.

Signed-off-by: default avatarGabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarAndy <Lutomirski&lt;luto@kernel.org>
Link: https://lore.kernel.org/r/20201004032536.1229030-10-krisman@collabora.com
parent 3316ec8c

arch/x86/entry/vsyscall/vsyscall_64.c

+1 −1
Original line number Diff line number Diff line
@@ -316,7 +316,7 @@ static struct vm_area_struct gate_vma __ro_after_init = { 
struct vm_area_struct *get_gate_vma(struct mm_struct *mm)

{

#ifdef CONFIG_COMPAT

	if (!mm || mm->context.ia32_compat)

	if (!mm || !(mm->context.flags & MM_CONTEXT_HAS_VSYSCALL))

		return NULL;

#endif

	if (vsyscall_mode == NONE)

arch/x86/include/asm/mmu.h

+7 −2
Original line number Diff line number Diff line
@@ -6,6 +6,12 @@ 
#include <linux/rwsem.h>

#include <linux/mutex.h>

#include <linux/atomic.h>

#include <linux/bits.h>



/* Uprobes on this MM assume 32-bit code */

#define MM_CONTEXT_UPROBE_IA32	BIT(0)

/* vsyscall page is accessible on this MM */

#define MM_CONTEXT_HAS_VSYSCALL	BIT(1)



/*

 * x86 has arch-specific MMU state beyond what lives in mm_struct.
@@ -33,8 +39,7 @@ typedef struct { 
#endif



#ifdef CONFIG_X86_64

	/* True if mm supports a task running in 32 bit compatibility mode. */

	unsigned short ia32_compat;

	unsigned short flags;

#endif



	struct mutex lock;

arch/x86/include/asm/mmu_context.h

+1 −1
Original line number Diff line number Diff line
@@ -177,7 +177,7 @@ static inline void arch_exit_mmap(struct mm_struct *mm) 
static inline bool is_64bit_mm(struct mm_struct *mm)

{

	return	!IS_ENABLED(CONFIG_IA32_EMULATION) ||

		!(mm->context.ia32_compat == TIF_IA32);

		!(mm->context.flags & MM_CONTEXT_UPROBE_IA32);

}

#else

static inline bool is_64bit_mm(struct mm_struct *mm)

arch/x86/kernel/process_64.c

+11 −6
Original line number Diff line number Diff line
@@ -646,10 +646,8 @@ void set_personality_64bit(void) 
	/* Pretend that this comes from a 64bit execve */

	task_pt_regs(current)->orig_ax = __NR_execve;

	current_thread_info()->status &= ~TS_COMPAT;



	/* Ensure the corresponding mm is not marked. */

	if (current->mm)

		current->mm->context.ia32_compat = 0;

		current->mm->context.flags = MM_CONTEXT_HAS_VSYSCALL;



	/* TBD: overwrites user setup. Should have two bits.

	   But 64bit processes have always behaved this way,
@@ -664,7 +662,8 @@ static void __set_personality_x32(void) 
	clear_thread_flag(TIF_IA32);

	set_thread_flag(TIF_X32);

	if (current->mm)

		current->mm->context.ia32_compat = TIF_X32;

		current->mm->context.flags = 0;



	current->personality &= ~READ_IMPLIES_EXEC;

	/*

	 * in_32bit_syscall() uses the presence of the x32 syscall bit
@@ -684,8 +683,14 @@ static void __set_personality_ia32(void) 
#ifdef CONFIG_IA32_EMULATION

	set_thread_flag(TIF_IA32);

	clear_thread_flag(TIF_X32);

	if (current->mm)

		current->mm->context.ia32_compat = TIF_IA32;

	if (current->mm) {

		/*

		 * uprobes applied to this MM need to know this and

		 * cannot use user_64bit_mode() at that time.

		 */

		current->mm->context.flags = MM_CONTEXT_UPROBE_IA32;

	}



	current->personality |= force_personality32;

	/* Prepare the first "return" to user space */

	task_pt_regs(current)->orig_ax = __NR_ia32_execve;

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