Subject: Re: [PATCHv7 2/3] x86/vdso: add mremap hook to vm_special_mapping
References: <1460987025-30360-2-git-send-email-dsafonov@virtuozzo.com>
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CC: <linux-kernel@vger.kernel.org>, <tglx@linutronix.de>, <mingo@redhat.com>,
        <hpa@zytor.com>, <x86@kernel.org>, <akpm@linux-foundation.org>,
        <linux-mm@kvack.org>, <0x7f454c46@gmail.com>
To: <luto@amacapital.net>
From: Dmitry Safonov <dsafonov@virtuozzo.com>
Message-ID: <5717ACD7.6080909@virtuozzo.com>
Date: Wed, 20 Apr 2016 19:22:47 +0300
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On 04/18/2016 05:23 PM, Dmitry Safonov wrote:
> Add possibility for userspace 32-bit applications to move
> vdso mapping. Previously, when userspace app called
> mremap for vdso, in return path it would land on previous
> address of vdso page, resulting in segmentation violation.
> Now it lands fine and returns to userspace with remapped vdso.
> This will also fix context.vdso pointer for 64-bit, which does not
> affect the user of vdso after mremap by now, but this may change.
>
> As suggested by Andy, return EINVAL for mremap that splits vdso image.
>
> Renamed and moved text_mapping structure declaration inside
> map_vdso, as it used only there and now it complement
> vvar_mapping variable.
>
> There is still problem for remapping vdso in glibc applications:
> linker relocates addresses for syscalls on vdso page, so
> you need to relink with the new addresses. Or the next syscall
> through glibc may fail:
>    Program received signal SIGSEGV, Segmentation fault.
>    #0  0xf7fd9b80 in __kernel_vsyscall ()
>    #1  0xf7ec8238 in _exit () from /usr/lib32/libc.so.6
>
> Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>

Andy, can I have an ack from you for this version?
If it looks fine for you, of course.
And for v5 test (3/3 patch)? (I did not resed it, as it hasn't changed)

> ---
> v7: that's just not my day: add new_vma parameter to vdso_fix_landing
>      sorry for the noise
> v6: moved vdso_image_32 check and fixup code into vdso_fix_landing function
>      with ifdefs around
> v5: as Andy suggested, add a check that new_vma->vm_mm and current->mm are
>      the same, also check not only in_ia32_syscall() but image == &vdso_image_32
> v4: drop __maybe_unused & use image from mm->context instead vdso_image_32
> v3: as Andy suggested, return EINVAL in case of splitting vdso blob on mremap;
>      used is_ia32_task instead of ifdefs
> v2: added __maybe_unused for pt_regs in vdso_mremap
>
>   arch/x86/entry/vdso/vma.c | 50 ++++++++++++++++++++++++++++++++++++++++++-----
>   include/linux/mm_types.h  |  3 +++
>   mm/mmap.c                 | 10 ++++++++++
>   3 files changed, 58 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
> index 10f704584922..d94291a19b6e 100644
> --- a/arch/x86/entry/vdso/vma.c
> +++ b/arch/x86/entry/vdso/vma.c
> @@ -12,6 +12,7 @@
>   #include <linux/random.h>
>   #include <linux/elf.h>
>   #include <linux/cpu.h>
> +#include <linux/ptrace.h>
>   #include <asm/pvclock.h>
>   #include <asm/vgtod.h>
>   #include <asm/proto.h>
> @@ -98,10 +99,43 @@ static int vdso_fault(const struct vm_special_mapping *sm,
>   	return 0;
>   }
>   
> -static const struct vm_special_mapping text_mapping = {
> -	.name = "[vdso]",
> -	.fault = vdso_fault,
> -};
> +#if defined CONFIG_X86_32 || defined CONFIG_COMPAT
> +static void vdso_fix_landing(const struct vdso_image *image,
> +		struct vm_area_struct *new_vma)
> +{
> +	if (in_ia32_syscall() && image == &vdso_image_32) {
> +		struct pt_regs *regs = current_pt_regs();
> +		unsigned long vdso_land = image->sym_int80_landing_pad;
> +		unsigned long old_land_addr = vdso_land +
> +			(unsigned long)current->mm->context.vdso;
> +
> +		/* Fixing userspace landing - look at do_fast_syscall_32 */
> +		if (regs->ip == old_land_addr)
> +			regs->ip = new_vma->vm_start + vdso_land;
> +	}
> +}
> +#else
> +static void vdso_fix_landing(const struct vdso_image *image,
> +		struct vm_area_struct *new_vma) {}
> +#endif
> +
> +static int vdso_mremap(const struct vm_special_mapping *sm,
> +		struct vm_area_struct *new_vma)
> +{
> +	unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
> +	const struct vdso_image *image = current->mm->context.vdso_image;
> +
> +	if (image->size != new_size)
> +		return -EINVAL;
> +
> +	if (current->mm != new_vma->vm_mm)
> +		return -EFAULT;
> +
> +	vdso_fix_landing(image, new_vma);
> +	current->mm->context.vdso = (void __user *)new_vma->vm_start;
> +
> +	return 0;
> +}
>   
>   static int vvar_fault(const struct vm_special_mapping *sm,
>   		      struct vm_area_struct *vma, struct vm_fault *vmf)
> @@ -162,6 +196,12 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
>   	struct vm_area_struct *vma;
>   	unsigned long addr, text_start;
>   	int ret = 0;
> +
> +	static const struct vm_special_mapping vdso_mapping = {
> +		.name = "[vdso]",
> +		.fault = vdso_fault,
> +		.mremap = vdso_mremap,
> +	};
>   	static const struct vm_special_mapping vvar_mapping = {
>   		.name = "[vvar]",
>   		.fault = vvar_fault,
> @@ -195,7 +235,7 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
>   				       image->size,
>   				       VM_READ|VM_EXEC|
>   				       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
> -				       &text_mapping);
> +				       &vdso_mapping);
>   
>   	if (IS_ERR(vma)) {
>   		ret = PTR_ERR(vma);
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index c2d75b4fa86c..4d16ab9287af 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -586,6 +586,9 @@ struct vm_special_mapping {
>   	int (*fault)(const struct vm_special_mapping *sm,
>   		     struct vm_area_struct *vma,
>   		     struct vm_fault *vmf);
> +
> +	int (*mremap)(const struct vm_special_mapping *sm,
> +		     struct vm_area_struct *new_vma);
>   };
>   
>   enum tlb_flush_reason {
> diff --git a/mm/mmap.c b/mm/mmap.c
> index bd2e1a533bc1..ba71658dd1a1 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2930,9 +2930,19 @@ static const char *special_mapping_name(struct vm_area_struct *vma)
>   	return ((struct vm_special_mapping *)vma->vm_private_data)->name;
>   }
>   
> +static int special_mapping_mremap(struct vm_area_struct *new_vma)
> +{
> +	struct vm_special_mapping *sm = new_vma->vm_private_data;
> +
> +	if (sm->mremap)
> +		return sm->mremap(sm, new_vma);
> +	return 0;
> +}
> +
>   static const struct vm_operations_struct special_mapping_vmops = {
>   	.close = special_mapping_close,
>   	.fault = special_mapping_fault,
> +	.mremap = special_mapping_mremap,
>   	.name = special_mapping_name,
>   };
>   


-- 
Regards,
Dmitry Safonov