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Message-ID: <160371675292.397.16758659806817657829.tip-bot2@tip-bot2>
Date: Mon, 26 Oct 2020 12:52:32 -0000
From: "tip-bot2 for Gabriel Krisman Bertazi" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Gabriel Krisman Bertazi <krisman@...labora.com>,
Thomas Gleixner <tglx@...utronix.de>,
Andy Lutomirski <luto@...nel.org>, x86 <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/cleanups] x86/mm: Convert mmu context ia32_compat into a
proper flags field
The following commit has been merged into the x86/cleanups branch of tip:
Commit-ID: ff170cd0595398a7b66cb40f249eb2f10c29b66d
Gitweb: https://git.kernel.org/tip/ff170cd0595398a7b66cb40f249eb2f10c29b66d
Author: Gabriel Krisman Bertazi <krisman@...labora.com>
AuthorDate: Sat, 03 Oct 2020 23:25:35 -04:00
Committer: Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Mon, 26 Oct 2020 13:46:47 +01:00
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: Gabriel Krisman Bertazi <krisman@...labora.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Andy Lutomirski<luto@...nel.org>
Link: https://lore.kernel.org/r/20201004032536.1229030-10-krisman@collabora.com
---
arch/x86/entry/vsyscall/vsyscall_64.c | 2 +-
arch/x86/include/asm/mmu.h | 9 +++++++--
arch/x86/include/asm/mmu_context.h | 2 +-
arch/x86/kernel/process_64.c | 17 +++++++++++------
4 files changed, 20 insertions(+), 10 deletions(-)
diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index 44c3310..1b40b92 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -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)
diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h
index 9257667..5d74946 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 d98016b..054a791 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 5fb4103..d6efaf6 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -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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