[tip:x86/mm] x86/mm: Make in_compat_syscall() work during exec
From: tip-bot for Dmitry Safonov
Date: Fri Mar 31 2017 - 11:02:42 EST
Commit-ID: ada26481dfe698ac64b4aaf19a726e66eb8508c6
Gitweb: http://git.kernel.org/tip/ada26481dfe698ac64b4aaf19a726e66eb8508c6
Author: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
AuthorDate: Fri, 31 Mar 2017 14:11:37 +0300
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 31 Mar 2017 16:53:02 +0200
x86/mm: Make in_compat_syscall() work during exec
The x86 mmap() code selects the mmap base for an allocation depending on
the bitness of the syscall. For 64bit sycalls it select mm->mmap_base and
for 32bit mm->mmap_compat_base.
On execve the registers of the task invoking exec() are copied to the child
pt_regs. So child->pt_regs->orig_ax contains the execve syscall number of the
parent.
exec() calls mmap() which in turn uses in_compat_syscall() to check whether
the mapping is for a 32bit or a 64bit task. The decision is made on the
following criteria:
ia32 child->thread.status & TS_COMPAT
x32 child->pt_regs.orig_ax & __X32_SYSCALL_BIT
ia64 !ia32 && !x32
child->thread.status is corretly set up in set_personality_*(), but the
syscall number in child->pt_regs.orig_ax is left unmodified.
Therefore the parent/child combinations work or fail in the following way:
Parent Child Child->thread_status child->pt_regs.orig_ax in_compat() Works
ia64 ia64 TS_COMPAT == 0 __X32_SYSCALL_BIT == 0 false Y
ia64 ia32 TS_COMPAT == 1 __X32_SYSCALL_BIT == 0 true Y
ia64 x32 TS_COMPAT == 0 __X32_SYSCALL_BIT == 0 false N
ia32 ia64 TS_COMPAT == 0 __X32_SYSCALL_BIT == 0 false Y
ia32 ia32 TS_COMPAT == 1 __X32_SYSCALL_BIT == 0 true Y
ia32 x32 TS_COMPAT == 0 __X32_SYSCALL_BIT == 0 false N
x32 ia64 TS_COMPAT == 0 __X32_SYSCALL_BIT == 1 true N
x32 ia32 TS_COMPAT == 1 __X32_SYSCALL_BIT == 1 true Y
x32 x32 TS_COMPAT == 0 __X32_SYSCALL_BIT == 1 true Y
Make set_personality_*() store the syscall number incl. __X32_SYSCALL_BIT
which corresponds to the newly started ELF executable in the childs
pt_regs, i.e. pretend that the exec was invoked from a task with the same
executable format.
So both thread.status and pt_regs.orig_ax correspond to the new ELF format
and in_compat_syscall() returns the correct result.
[ tglx: Rewrote changelog ]
Fixes: commit 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for 32-bit mmap()")
Reported-by: Adam Borowski <kilobyte@xxxxxxxxxx>
Suggested-by: H. Peter Anvin <hpa@xxxxxxxxx>
Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
Cc: 0x7f454c46@xxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: Andrei Vagin <avagin@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20170331111137.28170-1-dsafonov@xxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
arch/x86/kernel/process_64.c | 67 ++++++++++++++++++++++++++++++--------------
1 file changed, 46 insertions(+), 21 deletions(-)
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index ea1a618..825a1e4 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -53,6 +53,11 @@
#include <asm/xen/hypervisor.h>
#include <asm/vdso.h>
#include <asm/intel_rdt.h>
+#include <asm/unistd.h>
+#ifdef CONFIG_IA32_EMULATION
+/* Not included via unistd.h */
+#include <asm/unistd_32_ia32.h>
+#endif
__visible DEFINE_PER_CPU(unsigned long, rsp_scratch);
@@ -494,6 +499,8 @@ void set_personality_64bit(void)
clear_thread_flag(TIF_IA32);
clear_thread_flag(TIF_ADDR32);
clear_thread_flag(TIF_X32);
+ /* Pretend that this comes from a 64bit execve */
+ task_pt_regs(current)->orig_ax = __NR_execve;
/* Ensure the corresponding mm is not marked. */
if (current->mm)
@@ -506,32 +513,50 @@ void set_personality_64bit(void)
current->personality &= ~READ_IMPLIES_EXEC;
}
-void set_personality_ia32(bool x32)
+static void __set_personality_x32(void)
{
- /* inherit personality from parent */
+#ifdef CONFIG_X86_X32
+ clear_thread_flag(TIF_IA32);
+ set_thread_flag(TIF_X32);
+ if (current->mm)
+ current->mm->context.ia32_compat = TIF_X32;
+ current->personality &= ~READ_IMPLIES_EXEC;
+ /*
+ * in_compat_syscall() uses the presence of the x32 syscall bit
+ * flag to determine compat status. The x86 mmap() code relies on
+ * the syscall bitness so set x32 syscall bit right here to make
+ * in_compat_syscall() work during exec().
+ *
+ * Pretend to come from a x32 execve.
+ */
+ task_pt_regs(current)->orig_ax = __NR_x32_execve | __X32_SYSCALL_BIT;
+ current->thread.status &= ~TS_COMPAT;
+#endif
+}
+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;
+ current->personality |= force_personality32;
+ /* Prepare the first "return" to user space */
+ task_pt_regs(current)->orig_ax = __NR_ia32_execve;
+ current->thread.status |= TS_COMPAT;
+#endif
+}
+
+void set_personality_ia32(bool x32)
+{
/* Make sure to be in 32bit mode */
set_thread_flag(TIF_ADDR32);
- /* Mark the associated mm as containing 32-bit tasks. */
- if (x32) {
- clear_thread_flag(TIF_IA32);
- set_thread_flag(TIF_X32);
- if (current->mm)
- current->mm->context.ia32_compat = TIF_X32;
- current->personality &= ~READ_IMPLIES_EXEC;
- /* in_compat_syscall() uses the presence of the x32
- syscall bit flag to determine compat status */
- current->thread.status &= ~TS_COMPAT;
- } else {
- set_thread_flag(TIF_IA32);
- clear_thread_flag(TIF_X32);
- if (current->mm)
- current->mm->context.ia32_compat = TIF_IA32;
- current->personality |= force_personality32;
- /* Prepare the first "return" to user space */
- current->thread.status |= TS_COMPAT;
- }
+ if (x32)
+ __set_personality_x32();
+ else
+ __set_personality_ia32();
}
EXPORT_SYMBOL_GPL(set_personality_ia32);