Re: [PATCH] x86/mpx: fix recursive munmap() corruption

Laurent Dufour
2019-05-07T16:35:58Z

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Le 01/05/2019 à 12:32, Michael Ellerman a écrit :
> Laurent Dufour <ldufour@linux.vnet.ibm.com> writes:
>> Le 23/04/2019 à 18:04, Dave Hansen a écrit :
>>> On 4/23/19 4:16 AM, Laurent Dufour wrote:
> ...
>>>> There are 2 assumptions here:
>>>> 1. 'start' and 'end' are page aligned (this is guaranteed by __do_munmap().
>>>> 2. the VDSO is 1 page (this is guaranteed by the union vdso_data_store on powerpc)
>>>
>>> Are you sure about #2? The 'vdso64_pages' variable seems rather
>>> unnecessary if the VDSO is only 1 page. ;)
>>
>> Hum, not so sure now ;)
>> I got confused, only the header is one page.
>> The test is working as a best effort, and don't cover the case where
>> only few pages inside the VDSO are unmmapped (start >
>> mm->context.vdso_base). This is not what CRIU is doing and so this was
>> enough for CRIU support.
>>
>> Michael, do you think there is a need to manage all the possibility
>> here, since the only user is CRIU and unmapping the VDSO is not a so
>> good idea for other processes ?
>
> Couldn't we implement the semantic that if any part of the VDSO is
> unmapped then vdso_base is set to zero? That should be fairly easy, eg:
>
> if (start < vdso_end && end >= mm->context.vdso_base)
> mm->context.vdso_base = 0;
>
>
> We might need to add vdso_end to the mm->context, but that should be OK.
>
> That seems like it would work for CRIU and make sense in general?

Sorry for the late answer, yes this would make more sense.

Here is a patch doing that.

Cheers,
Laurent

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From 5b64a86c2a8042c7785c3d3f5e58e954a2c8c843 Mon Sep 17 00:00:00 2001
From: Laurent Dufour <ldufour@linux.ibm.com>
Date: Tue, 7 May 2019 16:29:46 +0200
Subject: [PATCH] powerpc/vdso: handle generic unmap of the VDSO

Make the unmap of the VDSO more generic by checking for the start and end
of the VDSO.

This implies to add the vdso_end address in the mm_context_t structure.

Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
---
arch/powerpc/include/asm/book3s/32/mmu-hash.h | 3 ++-
arch/powerpc/include/asm/book3s/64/mmu.h | 2 +-
arch/powerpc/include/asm/mm-arch-hooks.h | 5 ++++-
arch/powerpc/include/asm/mmu_context.h | 21 +++++++++++++++++--
arch/powerpc/include/asm/nohash/32/mmu-40x.h | 2 +-
arch/powerpc/include/asm/nohash/32/mmu-44x.h | 2 +-
arch/powerpc/include/asm/nohash/32/mmu-8xx.h | 2 +-
arch/powerpc/include/asm/nohash/mmu-book3e.h | 2 +-
arch/powerpc/kernel/vdso.c | 2 ++
9 files changed, 32 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/32/mmu-hash.h b/arch/powerpc/include/asm/book3s/32/mmu-hash.h
index 2e277ca0170f..452152b809fc 100644
--- a/arch/powerpc/include/asm/book3s/32/mmu-hash.h
+++ b/arch/powerpc/include/asm/book3s/32/mmu-hash.h
@@ -29,6 +29,7 @@
#define BPP_RX 0x01 /* Read only */
#define BPP_RW 0x02 /* Read/write */

+
#ifndef __ASSEMBLY__
/* Contort a phys_addr_t into the right format/bits for a BAT */
#ifdef CONFIG_PHYS_64BIT
@@ -90,7 +91,7 @@ struct hash_pte {

typedef struct {
unsigned long id;
- unsigned long vdso_base;
+ unsigned long vdso_base, vdso_end;
} mm_context_t;

void update_bats(void);
diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
index 74d24201fc4f..7a5a91a0696f 100644
--- a/arch/powerpc/include/asm/book3s/64/mmu.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu.h
@@ -120,7 +120,7 @@ typedef struct {
struct npu_context *npu_context;
struct hash_mm_context *hash_context;

- unsigned long vdso_base;
+ unsigned long vdso_base, vdso_end;
/*
* pagetable fragment support
*/
diff --git a/arch/powerpc/include/asm/mm-arch-hooks.h b/arch/powerpc/include/asm/mm-arch-hooks.h
index f2a2da895897..1e2d527d3d1f 100644
--- a/arch/powerpc/include/asm/mm-arch-hooks.h
+++ b/arch/powerpc/include/asm/mm-arch-hooks.h
@@ -16,12 +16,15 @@ static inline void arch_remap(struct mm_struct *mm,
unsigned long old_start, unsigned long old_end,
unsigned long new_start, unsigned long new_end)
{
+ unsigned long length = mm->context.vdso_end - mm->context.vdso_base;
/*
* mremap() doesn't allow moving multiple vmas so we can limit the
* check to old_start == vdso_base.
*/
- if (old_start == mm->context.vdso_base)
+ if (old_start == mm->context.vdso_base) {
+ mm->context.vdso_end = new_start + length;
mm->context.vdso_base = new_start;
+ }
}
#define arch_remap arch_remap

diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index 611204e588b9..c24f5ed0aeff 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -235,8 +235,25 @@ static inline void arch_unmap(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
- if (start <= mm->context.vdso_base && mm->context.vdso_base < end)
- mm->context.vdso_base = 0;
+ unsigned long vdso_base, vdso_end;
+
+ vdso_base = mm->context.vdso_base;
+ vdso_end = mm->context.vdso_end;
+
+ /*
+ * Partial unmapping of pages inside the VDSO, is consider equivalent
+ * to unmapping the VDSO.
+ *
+ * case 1 > | VDSO | <
+ * case 2 > | < |
+ * case 3 | > < |
+ * case 4 | > | <
+ */
+
+ if ((start <= vdso_base && vdso_end <= end) || /* 1 */
+ (vdso_base <= start && start < vdso_end) || /* 3,4 */
+ (vdso_base < end && end <= vdso_end)) /* 2,3 */
+ mm->context.vdso_base = mm->context.vdso_end = 0;
}

static inline void arch_bprm_mm_init(struct mm_struct *mm,
diff --git a/arch/powerpc/include/asm/nohash/32/mmu-40x.h b/arch/powerpc/include/asm/nohash/32/mmu-40x.h
index 74f4edb5916e..98739ba9d36e 100644
--- a/arch/powerpc/include/asm/nohash/32/mmu-40x.h
+++ b/arch/powerpc/include/asm/nohash/32/mmu-40x.h
@@ -57,7 +57,7 @@
typedef struct {
unsigned int id;
unsigned int active;
- unsigned long vdso_base;
+ unsigned long vdso_base, vdso_end;
} mm_context_t;

#endif /* !__ASSEMBLY__ */
diff --git a/arch/powerpc/include/asm/nohash/32/mmu-44x.h b/arch/powerpc/include/asm/nohash/32/mmu-44x.h
index 28aa3b339c5e..de1d5b1c8cec 100644
--- a/arch/powerpc/include/asm/nohash/32/mmu-44x.h
+++ b/arch/powerpc/include/asm/nohash/32/mmu-44x.h
@@ -108,7 +108,7 @@ extern unsigned int tlb_44x_index;
typedef struct {
unsigned int id;
unsigned int active;
- unsigned long vdso_base;
+ unsigned long vdso_base, vdso_end;
} mm_context_t;

/* patch sites */
diff --git a/arch/powerpc/include/asm/nohash/32/mmu-8xx.h b/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
index 76af5b0cb16e..414ce6638b20 100644
--- a/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
@@ -209,7 +209,7 @@ struct slice_mask {
typedef struct {
unsigned int id;
unsigned int active;
- unsigned long vdso_base;
+ unsigned long vdso_base, vdso_end;
#ifdef CONFIG_PPC_MM_SLICES
u16 user_psize; /* page size index */
unsigned char low_slices_psize[SLICE_ARRAY_SIZE];
diff --git a/arch/powerpc/include/asm/nohash/mmu-book3e.h b/arch/powerpc/include/asm/nohash/mmu-book3e.h
index 4c9777d256fb..8f406ad9fe25 100644
--- a/arch/powerpc/include/asm/nohash/mmu-book3e.h
+++ b/arch/powerpc/include/asm/nohash/mmu-book3e.h
@@ -229,7 +229,7 @@ extern unsigned int tlbcam_index;
typedef struct {
unsigned int id;
unsigned int active;
- unsigned long vdso_base;
+ unsigned long vdso_base, vdso_end;
} mm_context_t;

/* Page size definitions, common between 32 and 64-bit
diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index a31b6234fcd7..263f820cc666 100644
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -182,6 +182,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
#endif

current->mm->context.vdso_base = 0;
+ current->mm->context.vdso_end = 0;

/* vDSO has a problem and was disabled, just don't "enable" it for the
* process
@@ -217,6 +218,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
* will fail to recognise it as a vDSO (since arch_vma_name fails).
*/
current->mm->context.vdso_base = vdso_base;
+ current->mm->context.vdso_end = vdso_base + (vdso_pages << PAGE_SHIFT);

/*
* our vma flags don't have VM_WRITE so by default, the process isn't
--
2.21.0