From: Andy Lutomirski <luto@xxxxxxxxxx>
commit 35f1c89b0cce247bf0213df243ed902989b1dcda upstream.
The recent rework of probe_kernel_address() and its conversion to
get_kernel_nofault() inadvertently broke is_prefetch(). Before this
change, probe_kernel_address() was used as a sloppy "read user or
kernel memory" helper, but it doesn't do that any more. The new
get_kernel_nofault() reads *kernel* memory only, which completely broke
is_prefetch() for user access.
Adjust the code to the correct accessor based on access mode. The
manual address bounds check is no longer necessary, since the accessor
helpers (get_user() / get_kernel_nofault()) do the right thing all by
themselves. As a bonus, by using the correct accessor, the open-coded
address bounds check is not needed anymore.
[ bp: Massage commit message. ]
Fixes: eab0c6089b68 ("maccess: unify the probe kernel arch hooks")
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/b91f7f92f3367d2d3a88eec3b09c6aab1b2dc8ef.1612924255.git.luto@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/mm/fault.c | 27 +++++++++++++++++----------
1 file changed, 17 insertions(+), 10 deletions(-)
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -53,7 +53,7 @@ kmmio_fault(struct pt_regs *regs, unsign
* 32-bit mode:
*
* Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
- * Check that here and ignore it.
+ * Check that here and ignore it. This is AMD erratum #91.
*
* 64-bit mode:
*
@@ -82,11 +82,7 @@ check_prefetch_opcode(struct pt_regs *re
#ifdef CONFIG_X86_64
case 0x40:
/*
- * In AMD64 long mode 0x40..0x4F are valid REX prefixes
- * Need to figure out under what instruction mode the
- * instruction was issued. Could check the LDT for lm,
- * but for now it's good enough to assume that long
- * mode only uses well known segments or kernel.
+ * In 64-bit mode 0x40..0x4F are valid REX prefixes
*/
return (!user_mode(regs) || user_64bit_mode(regs));
#endif
@@ -126,20 +122,31 @@ is_prefetch(struct pt_regs *regs, unsign
instr = (void *)convert_ip_to_linear(current, regs);
max_instr = instr + 15;
- if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE_MAX)
- return 0;
+ /*
+ * This code has historically always bailed out if IP points to a
+ * not-present page (e.g. due to a race). No one has ever
+ * complained about this.
+ */
+ pagefault_disable();
while (instr < max_instr) {
unsigned char opcode;
- if (get_kernel_nofault(opcode, instr))
- break;
+ if (user_mode(regs)) {
+ if (get_user(opcode, instr))
+ break;
+ } else {
+ if (get_kernel_nofault(opcode, instr))
+ break;
+ }
instr++;
if (!check_prefetch_opcode(regs, instr, opcode, &prefetch))
break;
}
+
+ pagefault_enable();
return prefetch;
}
