[RFC,01/27] kernel: Export memory-management symbols required for KVM address space isolation

Commit Message

Alexandre Chartre May 13, 2019, 2:38 p.m. UTC

From: Liran Alon <[e-mail]>

Export symbols needed to create, manage, populate and switch
a mm from a kernel module (kvm in this case).

This is a hacky way for now to start.
This should be changed to some suitable memory-management API.

Signed-off-by: Liran Alon <[e-mail]>
Signed-off-by: Alexandre Chartre <[e-mail]>
---
 arch/x86/kernel/ldt.c |    1 +
 arch/x86/mm/tlb.c     |    3 ++-
 mm/memory.c           |    5 +++++
 3 files changed, 8 insertions(+), 1 deletions(-)

Comments

Peter Zijlstra May 13, 2019, 3:15 p.m. UTC | #1

On Mon, May 13, 2019 at 04:38:09PM +0200, Alexandre Chartre wrote:
> From: Liran Alon <[e-mail]>
> 
> Export symbols needed to create, manage, populate and switch
> a mm from a kernel module (kvm in this case).
> 
> This is a hacky way for now to start.
> This should be changed to some suitable memory-management API.

This should not be exported at all, ever, end of story.

Modules do not get to play with address spaces like that.

Liran Alon May 13, 2019, 3:17 p.m. UTC | #2

> On 13 May 2019, at 18:15, Peter Zijlstra <[e-mail]> wrote:
> 
> On Mon, May 13, 2019 at 04:38:09PM +0200, Alexandre Chartre wrote:
>> From: Liran Alon <[e-mail]>
>> 
>> Export symbols needed to create, manage, populate and switch
>> a mm from a kernel module (kvm in this case).
>> 
>> This is a hacky way for now to start.
>> This should be changed to some suitable memory-management API.
> 
> This should not be exported at all, ever, end of story.
> 
> Modules do not get to play with address spaces like that.

I agree… No doubt about that. This should never be merged like this.
It’s just to have an initial PoC of the concept so we can:
1) Messure performance impact of concept.
2) Get feedback on appropriate design and APIs from community.

-Liran

Patch

diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index b2463fc..19a86e0 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -401,6 +401,7 @@  void destroy_context_ldt(struct mm_struct *mm)
 	free_ldt_struct(mm->context.ldt);
 	mm->context.ldt = NULL;
 }
+EXPORT_SYMBOL_GPL(destroy_context_ldt);
 
 void ldt_arch_exit_mmap(struct mm_struct *mm)
 {
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 7f61431..a4db7f5 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -70,7 +70,7 @@  static void clear_asid_other(void)
 }
 
 atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1);
-
+EXPORT_SYMBOL_GPL(last_mm_ctx_id);
 
 static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen,
 			    u16 *new_asid, bool *need_flush)
@@ -159,6 +159,7 @@  void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 	switch_mm_irqs_off(prev, next, tsk);
 	local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(switch_mm);
 
 static void sync_current_stack_to_mm(struct mm_struct *mm)
 {
diff --git a/mm/memory.c b/mm/memory.c
index 36aac68..ede9335 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -434,6 +434,7 @@  int __pte_alloc(struct mm_struct *mm, pmd_t *pmd)
 		pte_free(mm, new);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(__pte_alloc);
 
 int __pte_alloc_kernel(pmd_t *pmd)
 {
@@ -453,6 +454,7 @@  int __pte_alloc_kernel(pmd_t *pmd)
 		pte_free_kernel(&init_mm, new);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(__pte_alloc_kernel);
 
 static inline void init_rss_vec(int *rss)
 {
@@ -4007,6 +4009,7 @@  int __p4d_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
 	spin_unlock(&mm->page_table_lock);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(__p4d_alloc);
 #endif /* __PAGETABLE_P4D_FOLDED */
 
 #ifndef __PAGETABLE_PUD_FOLDED
@@ -4039,6 +4042,7 @@  int __pud_alloc(struct mm_struct *mm, p4d_t *p4d, unsigned long address)
 	spin_unlock(&mm->page_table_lock);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(__pud_alloc);
 #endif /* __PAGETABLE_PUD_FOLDED */
 
 #ifndef __PAGETABLE_PMD_FOLDED
@@ -4072,6 +4076,7 @@  int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
 	spin_unlock(ptl);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(__pmd_alloc);
 #endif /* __PAGETABLE_PMD_FOLDED */
 
 static int __follow_pte_pmd(struct mm_struct *mm, unsigned long address,