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powerpc/32s: Prepare prevent_user_access() for user_access_end()

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In preparation of implementing user_access_begin and friends
on powerpc, the book3s/32 version of prevent_user_access() need
to be prepared for user_access_end().

user_access_end() doesn't provide the address and size which
were passed to user_access_begin(), required by prevent_user_access()
to know which segment to modify.

The list of segments which where unprotected by allow_user_access()
are available in current->kuap. But we don't want prevent_user_access()
to read this all the time, especially everytime it is 0 (for instance
because the access was not a write access).

Implement a special direction named KUAP_CURRENT. In this case only,
the addr and end are retrieved from current->kuap.

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/55bcc1f25d8200892a31f67a0b024ff3b816c3cc.1579866752.git.christophe.leroy@c-s.fr
This commit is contained in:
Christophe Leroy 2020-01-24 11:54:43 +00:00 committed by Michael Ellerman
parent 88f8c080d4
commit bedb4dbe44
3 changed files with 34 additions and 8 deletions
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27
arch/powerpc/include/asm/book3s/32/kup.h
View File

@ -108,6 +108,8 @@ static __always_inline void allow_user_access(void __user *to, const void __user
u32 addr, end;
BUILD_BUG_ON(!__builtin_constant_p(dir));
BUILD_BUG_ON(dir == KUAP_CURRENT);
if (!(dir & KUAP_WRITE))
return;
@ -117,6 +119,7 @@ static __always_inline void allow_user_access(void __user *to, const void __user
return;
end = min(addr + size, TASK_SIZE);
current->thread.kuap = (addr & 0xf0000000) | ((((end - 1) >> 28) + 1) & 0xf);
kuap_update_sr(mfsrin(addr) & ~SR_KS, addr, end); /* Clear Ks */
}
@ -127,15 +130,25 @@ static __always_inline void prevent_user_access(void __user *to, const void __us
u32 addr, end;
BUILD_BUG_ON(!__builtin_constant_p(dir));
if (!(dir & KUAP_WRITE))
if (dir == KUAP_CURRENT) {
u32 kuap = current->thread.kuap;
if (unlikely(!kuap))
return;
addr = kuap & 0xf0000000;
end = kuap << 28;
} else if (dir & KUAP_WRITE) {
addr = (__force u32)to;
end = min(addr + size, TASK_SIZE);
if (unlikely(addr >= TASK_SIZE || !size))
return;
} else {
return;
}
addr = (__force u32)to;
if (unlikely(addr >= TASK_SIZE || !size))
return;
end = min(addr + size, TASK_SIZE);
current->thread.kuap = 0;
kuap_update_sr(mfsrin(addr) | SR_KS, addr, end); /* set Ks */
}

4
arch/powerpc/include/asm/book3s/64/kup-radix.h
View File

@ -86,8 +86,10 @@ static __always_inline void allow_user_access(void __user *to, const void __user
set_kuap(AMR_KUAP_BLOCK_WRITE);
else if (dir == KUAP_WRITE)
set_kuap(AMR_KUAP_BLOCK_READ);
else
else if (dir == KUAP_READ_WRITE)
set_kuap(0);
else
BUILD_BUG();
}
static inline void prevent_user_access(void __user *to, const void __user *from,

11
arch/powerpc/include/asm/kup.h
View File

@ -5,6 +5,12 @@
#define KUAP_READ 1
#define KUAP_WRITE 2
#define KUAP_READ_WRITE (KUAP_READ | KUAP_WRITE)
/*
* For prevent_user_access() only.
* Use the current saved situation instead of the to/from/size params.
* Used on book3s/32
*/
#define KUAP_CURRENT 4
#ifdef CONFIG_PPC64
#include <asm/book3s/64/kup-radix.h>
@ -88,6 +94,11 @@ static inline void prevent_read_write_user(void __user *to, const void __user *f
prevent_user_access(to, from, size, KUAP_READ_WRITE);
}
static inline void prevent_current_access_user(void)
{
prevent_user_access(NULL, NULL, ~0UL, KUAP_CURRENT);
}
#endif /* !__ASSEMBLY__ */
#endif /* _ASM_POWERPC_KUAP_H_ */