From ada26481dfe698ac64b4aaf19a726e66eb8508c6 Mon Sep 17 00:00:00 2001 From: Dmitry Safonov Date: Fri, 31 Mar 2017 14:11:37 +0300 Subject: [PATCH] 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 Suggested-by: H. Peter Anvin Suggested-by: Thomas Gleixner Signed-off-by: Dmitry Safonov Cc: 0x7f454c46@gmail.com Cc: linux-mm@kvack.org Cc: Andrei Vagin Cc: Andy Lutomirski Cc: Cyrill Gorcunov Cc: Borislav Petkov Cc: "Kirill A. Shutemov" Link: http://lkml.kernel.org/r/20170331111137.28170-1-dsafonov@virtuozzo.com Signed-off-by: Thomas Gleixner --- 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 ea1a6180bf39..825a1e47cf3e 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -53,6 +53,11 @@ #include #include #include +#include +#ifdef CONFIG_IA32_EMULATION +/* Not included via unistd.h */ +#include +#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); -- 2.20.1