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powerpc: Implement user_access_save() and user_access_restore()

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Implement user_access_save() and user_access_restore()

On 8xx and radix:
  - On save, get the value of the associated special register then
    prevent user access.
  - On restore, set back the saved value to the associated special
    register.

On book3s/32:
  - On save, get the value stored in current->thread.kuap and prevent
    user access.
  - On restore, regenerate address range from the stored value and
    reopen read/write access for that range.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/54f2f74938006b33c55a416674807b42ef222068.1579866752.git.christophe.leroy@c-s.fr
This commit is contained in:
Christophe Leroy 2020-01-24 11:54:45 +00:00 committed by Michael Ellerman
parent 5cd623333e
commit 3d7dfd632f
5 changed files with 63 additions and 3 deletions
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23
arch/powerpc/include/asm/book3s/32/kup.h
View File

@ -153,6 +153,29 @@ static __always_inline void prevent_user_access(void __user *to, const void __us
kuap_update_sr(mfsrin(addr) | SR_KS, addr, end); /* set Ks */
}
static inline unsigned long prevent_user_access_return(void)
{
unsigned long flags = current->thread.kuap;
unsigned long addr = flags & 0xf0000000;
unsigned long end = flags << 28;
void __user *to = (__force void __user *)addr;
if (flags)
prevent_user_access(to, to, end - addr, KUAP_READ_WRITE);
return flags;
}
static inline void restore_user_access(unsigned long flags)
{
unsigned long addr = flags & 0xf0000000;
unsigned long end = flags << 28;
void __user *to = (__force void __user *)addr;
if (flags)
allow_user_access(to, to, end - addr, KUAP_READ_WRITE);
}
static inline bool
bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
{

22
arch/powerpc/include/asm/book3s/64/kup-radix.h
View File

@ -63,6 +63,14 @@
* because that would require an expensive read/modify write of the AMR.
*/
static inline unsigned long get_kuap(void)
{
if (!early_mmu_has_feature(MMU_FTR_RADIX_KUAP))
return 0;
return mfspr(SPRN_AMR);
}
static inline void set_kuap(unsigned long value)
{
if (!early_mmu_has_feature(MMU_FTR_RADIX_KUAP))
@ -98,6 +106,20 @@ static inline void prevent_user_access(void __user *to, const void __user *from,
set_kuap(AMR_KUAP_BLOCKED);
}
static inline unsigned long prevent_user_access_return(void)
{
unsigned long flags = get_kuap();
set_kuap(AMR_KUAP_BLOCKED);
return flags;
}
static inline void restore_user_access(unsigned long flags)
{
set_kuap(flags);
}
static inline bool
bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
{

2
arch/powerpc/include/asm/kup.h
View File

@ -55,6 +55,8 @@ static inline void allow_user_access(void __user *to, const void __user *from,
unsigned long size, unsigned long dir) { }
static inline void prevent_user_access(void __user *to, const void __user *from,
unsigned long size, unsigned long dir) { }
static inline unsigned long prevent_user_access_return(void) { return 0UL; }
static inline void restore_user_access(unsigned long flags) { }
static inline bool
bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
{

14
arch/powerpc/include/asm/nohash/32/kup-8xx.h
View File

@ -46,6 +46,20 @@ static inline void prevent_user_access(void __user *to, const void __user *from,
mtspr(SPRN_MD_AP, MD_APG_KUAP);
}
static inline unsigned long prevent_user_access_return(void)
{
unsigned long flags = mfspr(SPRN_MD_AP);
mtspr(SPRN_MD_AP, MD_APG_KUAP);
return flags;
}
static inline void restore_user_access(unsigned long flags)
{
mtspr(SPRN_MD_AP, flags);
}
static inline bool
bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
{

5
arch/powerpc/include/asm/uaccess.h
View File

@ -465,9 +465,8 @@ static __must_check inline bool user_access_begin(const void __user *ptr, size_t
}
#define user_access_begin user_access_begin
#define user_access_end prevent_current_access_user
static inline unsigned long user_access_save(void) { return 0UL; }
static inline void user_access_restore(unsigned long flags) { }
#define user_access_save prevent_user_access_return
#define user_access_restore restore_user_access
#define unsafe_op_wrap(op, err) do { if (unlikely(op)) goto err; } while (0)
#define unsafe_get_user(x, p, e) unsafe_op_wrap(__get_user_allowed(x, p), e)