This is a note to let you know that I've just added the patch titled
x86/mm: Convert mmu context ia32_compat into a proper flags field
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-mm-convert-mmu-context-ia32_compat-into-a-proper.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 1e6677766e249d2c21c8a5afde8e7dbb7da4cf70
Author: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
Date: Sat Oct 3 23:25:35 2020 -0400
x86/mm: Convert mmu context ia32_compat into a proper flags field
[ Upstream commit ff170cd0595398a7b66cb40f249eb2f10c29b66d ]
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: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Andy Lutomirski<luto@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20201004032536.1229030-10-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/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index f0b817eb6e8ba..c5d074f5627a4 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -292,7 +292,7 @@ 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)
diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h
index 9257667d13c5e..5d7494631ea95 100644
--- a/arch/x86/include/asm/mmu.h
+++ b/arch/x86/include/asm/mmu.h
@@ -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;
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index d98016b837559..054a791573231 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -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)
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 997d6556f4be8..8546dfd8683fc 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -644,10 +644,8 @@ 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,
@@ -662,7 +660,8 @@ 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
@@ -682,8 +681,14 @@ 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;
