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Date: Tue, 22 Jul 2014 00:50:18 +0000
From: "Zhang, Tianfei" <tianfei.zhang@...el.com>
To: "Ren, Qiaowei" <qiaowei.ren@...el.com>,
"H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"Hansen, Dave" <dave.hansen@...el.com>
CC: "x86@...nel.org" <x86@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"Ren, Qiaowei" <qiaowei.ren@...el.com>
Subject: RE: [PATCH v7 09/10] x86, mpx: cleanup unused bound tables
> -----Original Message-----
> From: owner-linux-mm@...ck.org [mailto:owner-linux-mm@...ck.org] On
> Behalf Of Qiaowei Ren
> Sent: Monday, July 21, 2014 1:39 PM
> To: H. Peter Anvin; Thomas Gleixner; Ingo Molnar; Hansen, Dave
> Cc: x86@...nel.org; linux-kernel@...r.kernel.org; linux-mm@...ck.org; Ren,
> Qiaowei
> Subject: [PATCH v7 09/10] x86, mpx: cleanup unused bound tables
>
> Since the kernel allocated those tables on-demand without userspace
> knowledge, it is also responsible for freeing them when the associated
> mappings go away.
>
> Here, the solution for this issue is to hook do_munmap() to check whether one
> process is MPX enabled. If yes, those bounds tables covered in the virtual
> address region which is being unmapped will be freed also.
>
> Signed-off-by: Qiaowei Ren <qiaowei.ren@...el.com>
> ---
> arch/x86/include/asm/mmu_context.h | 16 +++
> arch/x86/include/asm/mpx.h | 9 ++
> arch/x86/mm/mpx.c | 181
> ++++++++++++++++++++++++++++++++++++
> include/asm-generic/mmu_context.h | 6 +
> mm/mmap.c | 2 +
> 5 files changed, 214 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/include/asm/mmu_context.h
> b/arch/x86/include/asm/mmu_context.h
> index be12c53..af70d4f 100644
> --- a/arch/x86/include/asm/mmu_context.h
> +++ b/arch/x86/include/asm/mmu_context.h
> @@ -6,6 +6,7 @@
> #include <asm/pgalloc.h>
> #include <asm/tlbflush.h>
> #include <asm/paravirt.h>
> +#include <asm/mpx.h>
> #ifndef CONFIG_PARAVIRT
> #include <asm-generic/mm_hooks.h>
>
> @@ -96,4 +97,19 @@ do { \
> } while (0)
> #endif
>
> +static inline void arch_unmap(struct mm_struct *mm,
> + struct vm_area_struct *vma,
> + unsigned long start, unsigned long end) { #ifdef
> CONFIG_X86_INTEL_MPX
"#indef" new line
> + /*
> + * Check whether this vma comes from MPX-enabled application.
> + * If so, release this vma related bound tables.
> + */
> + if (mm->bd_addr && !(vma->vm_flags & VM_MPX))
> + mpx_unmap(mm, start, end);
> +
> +#endif
> +}
> +
> #endif /* _ASM_X86_MMU_CONTEXT_H */
> diff --git a/arch/x86/include/asm/mpx.h b/arch/x86/include/asm/mpx.h index
> 6cb0853..e848a74 100644
> --- a/arch/x86/include/asm/mpx.h
> +++ b/arch/x86/include/asm/mpx.h
> @@ -42,6 +42,13 @@
> #define MPX_BD_SIZE_BYTES
> (1UL<<(MPX_BD_ENTRY_OFFSET+MPX_BD_ENTRY_SHIFT))
> #define MPX_BT_SIZE_BYTES
> (1UL<<(MPX_BT_ENTRY_OFFSET+MPX_BT_ENTRY_SHIFT))
>
> +#define MPX_BD_ENTRY_MASK ((1<<MPX_BD_ENTRY_OFFSET)-1)
> +#define MPX_BT_ENTRY_MASK ((1<<MPX_BT_ENTRY_OFFSET)-1)
> +#define MPX_GET_BD_ENTRY_OFFSET(addr)
> ((((addr)>>(MPX_BT_ENTRY_OFFSET+ \
> + MPX_IGN_BITS)) & MPX_BD_ENTRY_MASK) <<
> MPX_BD_ENTRY_SHIFT)
> +#define MPX_GET_BT_ENTRY_OFFSET(addr) ((((addr)>>MPX_IGN_BITS) & \
> + MPX_BT_ENTRY_MASK) << MPX_BT_ENTRY_SHIFT)
> +
> #define MPX_BNDSTA_ERROR_CODE 0x3
> #define MPX_BNDCFG_ENABLE_FLAG 0x1
> #define MPX_BD_ENTRY_VALID_FLAG 0x1
> @@ -63,6 +70,8 @@ struct mpx_insn {
> #define MAX_MPX_INSN_SIZE 15
>
> unsigned long mpx_mmap(unsigned long len);
> +void mpx_unmap(struct mm_struct *mm,
> + unsigned long start, unsigned long end);
>
> #ifdef CONFIG_X86_INTEL_MPX
> int do_mpx_bt_fault(struct xsave_struct *xsave_buf); diff --git
> a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index e1b28e6..d29ec9c 100644
> --- a/arch/x86/mm/mpx.c
> +++ b/arch/x86/mm/mpx.c
> @@ -2,6 +2,7 @@
> #include <linux/syscalls.h>
> #include <asm/mpx.h>
> #include <asm/mman.h>
> +#include <asm/mmu_context.h>
> #include <linux/sched/sysctl.h>
>
> static const char *mpx_mapping_name(struct vm_area_struct *vma) @@
> -77,3 +78,183 @@ out:
> up_write(&mm->mmap_sem);
> return ret;
> }
> +
> +/*
> + * Get the base of bounds tables pointed by specific bounds
> + * directory entry.
> + */
> +static int get_bt_addr(long __user *bd_entry, unsigned long *bt_addr,
> + unsigned int *valid)
> +{
> + if (get_user(*bt_addr, bd_entry))
> + return -EFAULT;
> +
> + *valid = *bt_addr & MPX_BD_ENTRY_VALID_FLAG;
> + *bt_addr &= MPX_BT_ADDR_MASK;
> +
> + /*
> + * If this bounds directory entry is nonzero, and meanwhile
> + * the valid bit is zero, one SIGSEGV will be produced due to
> + * this unexpected situation.
> + */
> + if (!(*valid) && *bt_addr)
> + force_sig(SIGSEGV, current);
> +
> + return 0;
> +}
> +
> +/*
> + * Free the backing physical pages of bounds table 'bt_addr'.
> + * Assume start...end is within that bounds table.
> + */
> +static void zap_bt_entries(struct mm_struct *mm, unsigned long bt_addr,
> + unsigned long start, unsigned long end) {
> + struct vm_area_struct *vma;
> +
> + /* Find the vma which overlaps this bounds table */
> + vma = find_vma(mm, bt_addr);
> + if (!vma || vma->vm_start > bt_addr ||
> + vma->vm_end < bt_addr+MPX_BT_SIZE_BYTES)
> + return;
> +
> + zap_page_range(vma, start, end, NULL); }
> +
> +static void unmap_single_bt(struct mm_struct *mm, long __user *bd_entry,
> + unsigned long bt_addr)
> +{
> + if (user_atomic_cmpxchg_inatomic(&bt_addr, bd_entry,
> + bt_addr | MPX_BD_ENTRY_VALID_FLAG, 0))
> + return;
> +
> + /*
> + * to avoid recursion, do_munmap() will check whether it comes
> + * from one bounds table through VM_MPX flag.
> + */
> + do_munmap(mm, bt_addr & MPX_BT_ADDR_MASK,
> MPX_BT_SIZE_BYTES); }
> +
> +/*
> + * If the bounds table pointed by bounds directory 'bd_entry' is
> + * not shared, unmap this whole bounds table. Otherwise, only free
> + * those backing physical pages of bounds table entries covered
> + * in this virtual address region start...end.
> + */
> +static void unmap_shared_bt(struct mm_struct *mm, long __user *bd_entry,
> + unsigned long start, unsigned long end,
> + bool prev_shared, bool next_shared)
> +{
> + unsigned long bt_addr;
> + unsigned int bde_valid = 0;
> +
> + if (get_bt_addr(bd_entry, &bt_addr, &bde_valid) || !bde_valid)
> + return;
> +
> + if (prev_shared && next_shared)
> + zap_bt_entries(mm, bt_addr,
> + bt_addr+MPX_GET_BT_ENTRY_OFFSET(start),
> + bt_addr+MPX_GET_BT_ENTRY_OFFSET(end-1));
> + else if (prev_shared)
> + zap_bt_entries(mm, bt_addr,
> + bt_addr+MPX_GET_BT_ENTRY_OFFSET(start),
> + bt_addr+MPX_BT_SIZE_BYTES);
> + else if (next_shared)
> + zap_bt_entries(mm, bt_addr, bt_addr,
> + bt_addr+MPX_GET_BT_ENTRY_OFFSET(end-1));
> + else
> + unmap_single_bt(mm, bd_entry, bt_addr); }
"}" new line
> +
> +/*
> + * A virtual address region being munmap()ed might share bounds table
> + * with adjacent VMAs. We only need to free the backing physical
> + * memory of these shared bounds tables entries covered in this virtual
> + * address region.
> + *
> + * the VMAs covering the virtual address region start...end have
> +already
> + * been split if necessary and removed from the VMA list.
> + */
> +static void unmap_side_bts(struct mm_struct *mm, unsigned long start,
> + unsigned long end)
> +{
> + long __user *bde_start, *bde_end;
> + struct vm_area_struct *prev, *next;
> + bool prev_shared = false, next_shared = false;
> +
> + bde_start = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(start);
> + bde_end = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(end-1);
> +
> + /*
> + * Check whether bde_start and bde_end are shared with adjacent
> + * VMAs. Because the VMAs covering the virtual address region
> + * start...end have already been removed from the VMA list, if
> + * next is not NULL it will satisfy start < end <= next->vm_start.
> + * And if prev is not NULL, prev->vm_end <= start < end.
> + */
> + next = find_vma_prev(mm, start, &prev);
> + if (prev && MPX_GET_BD_ENTRY_OFFSET(prev->vm_end-1) ==
> (long)bde_start)
> + prev_shared = true;
> + if (next && MPX_GET_BD_ENTRY_OFFSET(next->vm_start) ==
> (long)bde_end)
> + next_shared = true;
> +
> + /*
> + * This virtual address region being munmap()ed is only
> + * covered by one bounds table.
> + *
> + * In this case, if this table is also shared with adjacent
> + * VMAs, only part of the backing physical memory of the bounds
> + * table need be freeed. Otherwise the whole bounds table need
> + * be unmapped.
> + */
> + if (bde_start == bde_end) {
> + unmap_shared_bt(mm, bde_start, start, end,
> + prev_shared, next_shared);
> + return;
> + }
> +
> + /*
> + * If more than one bounds tables are covered in this virtual
> + * address region being munmap()ed, we need to separately check
> + * whether bde_start and bde_end are shared with adjacent VMAs.
> + */
> + unmap_shared_bt(mm, bde_start, start, end, prev_shared, false);
> + unmap_shared_bt(mm, bde_end, start, end, false, next_shared); }
> +
> +/*
> + * Free unused bounds tables covered in a virtual address region being
> + * munmap()ed. Assume end > start.
> + *
> + * This function will be called by do_munmap(), and the VMAs covering
> + * the virtual address region start...end have already been split if
> + * necessary and remvoed from the VMA list.
> + */
> +void mpx_unmap(struct mm_struct *mm,
> + unsigned long start, unsigned long end) {
> + long __user *bd_entry, *bde_start, *bde_end;
> + unsigned long bt_addr;
> + unsigned int bde_valid;
> +
> + /*
> + * unmap bounds tables pointed out by start/end bounds directory
> + * entries, or only free part of their backing physical memroy
> + * if they are shared with adjacent VMAs.
> + */
> + unmap_side_bts(mm, start, end);
> +
> + /*
> + * unmap those bounds table which are entirely covered in this
> + * virtual address region.
> + */
> + bde_start = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(start);
> + bde_end = mm->bd_addr + MPX_GET_BD_ENTRY_OFFSET(end-1);
> + for (bd_entry = bde_start + 1; bd_entry < bde_end; bd_entry++) {
> + if (get_bt_addr(bd_entry, &bt_addr, &bde_valid))
> + return;
> + if (!bde_valid)
> + continue;
> + unmap_single_bt(mm, bd_entry, bt_addr);
> + }
> +}
> diff --git a/include/asm-generic/mmu_context.h
> b/include/asm-generic/mmu_context.h
> index a7eec91..ac558ca 100644
> --- a/include/asm-generic/mmu_context.h
> +++ b/include/asm-generic/mmu_context.h
> @@ -42,4 +42,10 @@ static inline void activate_mm(struct mm_struct
> *prev_mm, { }
>
> +static inline void arch_unmap(struct mm_struct *mm,
> + struct vm_area_struct *vma,
> + unsigned long start, unsigned long end) { }
> +
> #endif /* __ASM_GENERIC_MMU_CONTEXT_H */ diff --git a/mm/mmap.c
> b/mm/mmap.c index 129b847..8550d84 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2560,6 +2560,8 @@ int do_munmap(struct mm_struct *mm, unsigned
> long start, size_t len)
> /* Fix up all other VM information */
> remove_vma_list(mm, vma);
>
> + arch_unmap(mm, vma, start, end);
> +
> return 0;
> }
>
> --
> 1.7.1
>
> --
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