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x86: mm: remove architecture-specific 'access_ok()' define

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There's already a generic definition of 'access_ok()' in the
asm-generic/access_ok.h header file, and the only difference bwteen that
and the x86-specific one is the added check for WARN_ON_IN_IRQ().

And it turns out that the reason for that check is long gone: it used to
use a "user_addr_max()" inline function that depended on the current
thread, and caused problems in non-thread contexts.

For details, see commits 7c4788950b ("x86/uaccess, sched/preempt:
Verify access_ok() context") and in particular commit ae31fe51a3
("perf/x86: Restore TASK_SIZE check on frame pointer") about how and why
this came to be.

But that "current task" issue was removed in the big set_fs() removal by
Christoph Hellwig in commit 47058bb54b ("x86: remove address space
overrides using set_fs()").

So the reason for the test and the architecture-specific access_ok()
define no longer exists, and is actually harmful these days.  For
example, it led various 'copy_from_user_nmi()' games (eg using
__range_not_ok() instead, and then later converted to __access_ok() when
that became ok).

And that in turn meant that LAM was broken for the frame following
before this series, because __access_ok() used to not do the address
untagging.

Accessing user state still needs care in many contexts, but access_ok()
is not the place for this test.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Linus Torvalds torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2023-05-02 12:35:01 -07:00
parent 6014bc2756
commit 6ccdc91d6a
1 changed files with 0 additions and 34 deletions
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34
arch/x86/include/asm/uaccess.h
View File

@ -16,14 +16,6 @@
#include <asm/extable.h>
#include <asm/tlbflush.h>
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
static inline bool pagefault_disabled(void);
# define WARN_ON_IN_IRQ() \
WARN_ON_ONCE(!in_task() && !pagefault_disabled())
#else
# define WARN_ON_IN_IRQ()
#endif
#ifdef CONFIG_ADDRESS_MASKING
/*
* Mask out tag bits from the address.
@ -103,32 +95,6 @@ static inline bool __access_ok(const void __user *ptr, unsigned long size)
#define __access_ok __access_ok
#endif
/**
* access_ok - Checks if a user space pointer is valid
* @addr: User space pointer to start of block to check
* @size: Size of block to check
*
* Context: User context only. This function may sleep if pagefaults are
* enabled.
*
* Checks if a pointer to a block of memory in user space is valid.
*
* Note that, depending on architecture, this function probably just
* checks that the pointer is in the user space range - after calling
* this function, memory access functions may still return -EFAULT.
*
* Return: true (nonzero) if the memory block may be valid, false (zero)
* if it is definitely invalid.
*
* This should not be x86-specific. The only odd things out here is
* the WARN_ON_IN_IRQ(), which doesn't exist in the generic version.
*/
#define access_ok(addr, size) \
({ \
WARN_ON_IN_IRQ(); \
likely(__access_ok(addr, size)); \
})
#include <asm-generic/access_ok.h>
extern int __get_user_1(void);