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Date: Wed, 6 Apr 2016 11:04:23 -0700
From: Andy Lutomirski <luto@...capital.net>
To: Dmitry Safonov <dsafonov@...tuozzo.com>
Cc: Shuah Khan <shuahkh@....samsung.com>,
"H. Peter Anvin" <hpa@...or.com>, 0x7f454c46@...il.com,
khorenko@...tuozzo.com,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Cyrill Gorcunov <gorcunov@...nvz.org>,
Borislav Petkov <bp@...en8.de>, xemul@...tuozzo.com,
linux-kselftest@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
X86 ML <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>,
Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 1/2] x86/arch_prctl: add ARCH_SET_{COMPAT,NATIVE} to
change compatible mode
[cc Dave Hansen for MPX]
On Apr 6, 2016 9:30 AM, "Dmitry Safonov" <dsafonov@...tuozzo.com> wrote:
>
> Now each process that runs natively on x86_64 may execute 32-bit code
> by proper setting it's CS selector: either from LDT or reuse Linux's
> USER32_CS. The vice-versa is also valid: running 64-bit code in
> compatible task is also possible by choosing USER_CS.
> So we may switch between 32 and 64 bit code execution in any process.
> Linux will choose the right syscall numbers in entries for those
> processes. But it still will consider them native/compat by the
> personality, that elf loader set on launch. This affects i.e., ptrace
> syscall on those tasks: PTRACE_GETREGSET will return 64/32-bit regset
> according to process's mode (that's how strace detect task's
> personality from 4.8 version).
>
> This patch adds arch_prctl calls for x86 that make possible to tell
> Linux kernel in which mode the application is running currently.
> Mainly, this is needed for CRIU: restoring compatible & native
> applications both from 64-bit restorer. By that reason I wrapped all
> the code in CONFIG_CHECKPOINT_RESTORE.
> This patch solves also a problem for running 64-bit code in 32-bit elf
> (and reverse), that you have only 32-bit elf vdso for fast syscalls.
> When switching between native <-> compat mode by arch_prctl, it will
> remap needed vdso binary blob for target mode.
General comments first:
You forgot about x32.
I think that you should separate vdso remapping from "personality".
vdso remapping should be available even on native 32-bit builds, which
means that either you can't use arch_prctl for it or you'll have to
wire up arch_prctl as a 32-bit syscall.
For "personality", someone needs to enumerate all of the various thigs
that try to track bitness and see how many of them even make sense.
On brief inspection:
- TIF_IA32: affects signal format and does something to ptrace. I
suspect that whatever it does to ptrace is nonsensical, and I don't
know whether we're stuck with it.
- TIF_ADDR32 affects TASK_SIZE and mmap behavior (and the latter
isn't even done in a sensible way).
- is_64bit_mm affects MPX and uprobes.
On even more brief inspection:
- uprobes using is_64bit_mm is buggy.
- I doubt that having TASK_SIZE vary serves any purpose. Does anyone
know why TASK_SIZE is different for different tasks? It would save
code size and speed things up if TASK_SIZE were always TASK_SIZE_MAX.
- Using TIF_IA32 for signal processing is IMO suboptimal. Instead,
we should record which syscall installed the signal handler and use
the corresponding frame format.
- Using TIF_IA32 of the *target* for ptrace is nonsense. Having
strace figure out syscall type using that is actively buggy, and I ran
into that bug a few days ago and cursed at it. strace should inspect
TS_COMPAT (I don't know how, but that's what should happen). We may
be stuck with this for ABI reasons.
- For MPX, could we track which syscall called mpx_enable_management?
I.e. can we stash in_compat_syscall's return from
mpx_enable_management and use that instead of trying to determine the
MPX data structure format by the mm's initial type?
If we make all of these changes, we're left with *only* the ptrace
thing, and you could certainly add a way for CRIU to switch that
around.
>
> Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
> Cc: Pavel Emelyanov <xemul@...tuozzo.com>
> Cc: Konstantin Khorenko <khorenko@...tuozzo.com>
> CC: Dmitry Safonov <0x7f454c46@...il.com>
> Signed-off-by: Dmitry Safonov <dsafonov@...tuozzo.com>
> ---
> arch/x86/entry/vdso/vma.c | 76 ++++++++++++++++++++++++++--------
> arch/x86/include/asm/vdso.h | 5 +++
> arch/x86/include/uapi/asm/prctl.h | 6 +++
> arch/x86/kernel/process_64.c | 87 +++++++++++++++++++++++++++++++++++++++
> 4 files changed, 157 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
> index 10f704584922..9a1561da0bad 100644
> --- a/arch/x86/entry/vdso/vma.c
> +++ b/arch/x86/entry/vdso/vma.c
> @@ -156,22 +156,21 @@ static int vvar_fault(const struct vm_special_mapping *sm,
> return VM_FAULT_SIGBUS;
> }
>
> -static int map_vdso(const struct vdso_image *image, bool calculate_addr)
> +static int do_map_vdso(const struct vdso_image *image, bool calculate_addr,
> + unsigned long addr)
> {
> struct mm_struct *mm = current->mm;
> struct vm_area_struct *vma;
> - unsigned long addr, text_start;
> + unsigned long text_start;
> int ret = 0;
> static const struct vm_special_mapping vvar_mapping = {
> .name = "[vvar]",
> .fault = vvar_fault,
> };
>
> - if (calculate_addr) {
> + if (calculate_addr && !addr) {
> addr = vdso_addr(current->mm->start_stack,
> image->size - image->sym_vvar_start);
> - } else {
> - addr = 0;
> }
>
This is overcomplicated. Just pass in the address and us it as supplied.
> down_write(&mm->mmap_sem);
> @@ -209,11 +208,11 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
> VM_PFNMAP,
> &vvar_mapping);
>
> - if (IS_ERR(vma)) {
> + if (IS_ERR(vma))
> ret = PTR_ERR(vma);
> - goto up_fail;
> - }
>
> + if (ret)
> + do_munmap(mm, addr, image->size - image->sym_vvar_start);
> up_fail:
> if (ret)
> current->mm->context.vdso = NULL;
> @@ -223,24 +222,28 @@ up_fail:
> }
>
> #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
> -static int load_vdso32(void)
> +static int load_vdso32(unsigned long addr)
> {
> if (vdso32_enabled != 1) /* Other values all mean "disabled" */
> return 0;
>
> - return map_vdso(&vdso_image_32, false);
> + return do_map_vdso(&vdso_image_32, false, addr);
> }
> #endif
I'd just make it one function do_map_vdso(type, addr).
>
> #ifdef CONFIG_X86_64
> -int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
> +static int load_vdso64(unsigned long addr)
> {
> if (!vdso64_enabled)
> return 0;
>
> - return map_vdso(&vdso_image_64, true);
> + return do_map_vdso(&vdso_image_64, true, addr);
> }
>
> +int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
> +{
> + return load_vdso64(0);
> +}
> #ifdef CONFIG_COMPAT
> int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
> int uses_interp)
> @@ -250,20 +253,59 @@ int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
> if (!vdso64_enabled)
> return 0;
>
> - return map_vdso(&vdso_image_x32, true);
> + return do_map_vdso(&vdso_image_x32, true, 0);
> }
> #endif
> #ifdef CONFIG_IA32_EMULATION
> - return load_vdso32();
> + return load_vdso32(0);
No special 0 please.
> #else
> return 0;
> #endif
> }
> -#endif
> -#else
> +#endif /* CONFIG_COMPAT */
> +
> +#if defined(CONFIG_IA32_EMULATION) && defined(CONFIG_CHECKPOINT_RESTORE)
> +unsigned long unmap_vdso(void)
> +{
> + struct vm_area_struct *vma;
> + unsigned long addr = (unsigned long)current->mm->context.vdso;
> +
> + if (!addr)
> + return 0;
> +
> + /* vvar pages */
> + vma = find_vma(current->mm, addr - 1);
> + if (vma)
> + vm_munmap(vma->vm_start, vma->vm_end - vma->vm_start);
> +
> + /* vdso pages */
> + vma = find_vma(current->mm, addr);
> + if (vma)
> + vm_munmap(vma->vm_start, vma->vm_end - vma->vm_start);
> +
> + current->mm->context.vdso = NULL;
> +
> + return addr;
> +}
> +/*
> + * Maps needed vdso type: vdso_image_32/vdso_image_64
> + * @compatible - true for compatible, false for native vdso image
> + * @addr - specify addr for vdso mapping (0 for random/searching)
> + * NOTE: be sure to set/clear thread-specific flags before
> + * calling this function.
> + */
> +int map_vdso(bool compatible, unsigned long addr)
> +{
> + if (compatible)
> + return load_vdso32(addr);
> + else
> + return load_vdso64(addr);
> +}
This makes sense. But it can't be bool -- you forgot x32.
> +#endif /* CONFIG_IA32_EMULATION && CONFIG_CHECKPOINT_RESTORE */
> +#else /* !CONFIG_X86_64 */
> int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
> {
> - return load_vdso32();
> + return load_vdso32(0);
> }
> #endif
>
> diff --git a/arch/x86/include/asm/vdso.h b/arch/x86/include/asm/vdso.h
> index 43dc55be524e..3ead7cc48a68 100644
> --- a/arch/x86/include/asm/vdso.h
> +++ b/arch/x86/include/asm/vdso.h
> @@ -39,6 +39,11 @@ extern const struct vdso_image vdso_image_x32;
> extern const struct vdso_image vdso_image_32;
> #endif
>
> +#if defined(CONFIG_IA32_EMULATION) && defined(CONFIG_CHECKPOINT_RESTORE)
> +extern int map_vdso(bool to_compat, unsigned long addr);
> +extern unsigned long unmap_vdso(void);
> +#endif
> +
> extern void __init init_vdso_image(const struct vdso_image *image);
>
> #endif /* __ASSEMBLER__ */
> diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
> index 3ac5032fae09..455844f06485 100644
> --- a/arch/x86/include/uapi/asm/prctl.h
> +++ b/arch/x86/include/uapi/asm/prctl.h
> @@ -6,4 +6,10 @@
> #define ARCH_GET_FS 0x1003
> #define ARCH_GET_GS 0x1004
>
> +#if defined(CONFIG_IA32_EMULATION) && defined(CONFIG_CHECKPOINT_RESTORE)
> +#define ARCH_SET_COMPAT 0x2001
> +#define ARCH_SET_NATIVE 0x2002
> +#define ARCH_GET_PERSONALITY 0x2003
> +#endif
> +
> #endif /* _ASM_X86_PRCTL_H */
> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> index 6cbab31ac23a..e50660d59530 100644
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -49,6 +49,7 @@
> #include <asm/debugreg.h>
> #include <asm/switch_to.h>
> #include <asm/xen/hypervisor.h>
> +#include <asm/vdso.h>
>
> asmlinkage extern void ret_from_fork(void);
>
> @@ -505,6 +506,83 @@ void set_personality_ia32(bool x32)
> }
> EXPORT_SYMBOL_GPL(set_personality_ia32);
>
> +#if defined(CONFIG_IA32_EMULATION) && defined(CONFIG_CHECKPOINT_RESTORE)
> +/*
> + * Check if there are still some vmas (except vdso) for current,
> + * which placed above compatible TASK_SIZE.
> + * Check also code, data, stack, args and env placements.
> + * Returns true if all mappings are compatible.
> + */
> +static bool task_mappings_compatible(void)
> +{
> + struct mm_struct *mm = current->mm;
> + unsigned long top_addr = IA32_PAGE_OFFSET;
> + struct vm_area_struct *vma = find_vma(mm, top_addr);
> +
> + if (mm->end_code > top_addr ||
> + mm->end_data > top_addr ||
> + mm->start_stack > top_addr ||
> + mm->brk > top_addr ||
> + mm->arg_end > top_addr ||
> + mm->env_end > top_addr)
> + return false;
> +
> + while (vma) {
> + if ((vma->vm_start != (unsigned long)mm->context.vdso) &&
> + (vma->vm_end != (unsigned long)mm->context.vdso))
> + return false;
> +
> + top_addr = vma->vm_end;
> + vma = find_vma(mm, top_addr);
> + }
> +
> + return true;
> +}
What goes wrong if there are leftover high mappings?
> +
> +static int do_set_personality(bool compat, unsigned long addr)
> +{
> + int ret;
> + unsigned long old_vdso_base;
> + unsigned long old_mmap_base = current->mm->mmap_base;
> +
> + if (test_thread_flag(TIF_IA32) == compat) /* nothing to do */
> + return 0;
Please don't. Instead, remove TIF_IA32 entirely.
Also, please separate out ARCH_REMAP_VDSO from any personality change API.
> +
> + if (compat && !task_mappings_compatible())
> + return -EFAULT;
> +
> + /*
> + * We can't just remap vdso to needed location:
> + * vdso compatible and native images differs
> + */
> + old_vdso_base = unmap_vdso();
> +
> + if (compat)
> + set_personality_ia32(false);
> + else
> + set_personality_64bit();
> +
> + /*
> + * Update mmap_base & get_unmapped_area helper, side effect:
> + * one may change get_unmapped_area or mmap_base with personality()
> + * or switching to and fro compatible mode
> + */
> + arch_pick_mmap_layout(current->mm);
> +
> + ret = map_vdso(compat, addr);
> + if (ret) {
> + current->mm->mmap_base = old_mmap_base;
> + if (compat)
> + set_personality_64bit();
> + else
> + set_personality_ia32(false);
> + WARN_ON(map_vdso(!compat, old_vdso_base));
> + }
> +
> + return ret;
> +}
> +#endif
> +
> long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
> {
> int ret = 0;
> @@ -592,6 +670,15 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
> break;
> }
>
> +#if defined(CONFIG_IA32_EMULATION) && defined(CONFIG_CHECKPOINT_RESTORE)
> + case ARCH_SET_COMPAT:
> + return do_set_personality(true, addr);
> + case ARCH_SET_NATIVE:
> + return do_set_personality(false, addr);
> + case ARCH_GET_PERSONALITY:
> + return test_thread_flag(TIF_IA32);
> +#endif
> +
> default:
> ret = -EINVAL;
> break;
> --
> 2.7.4
>
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