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powerpc/603: Clear C bit when PTE is read only 

On book3s/32 MMU, PP bits don't offer kernel RO protection,
kernel pages are always RW.

However, on the 603 a page fault is always generated when the
C bit (change bit = dirty bit) is not set.

Enforce kernel RO protection by clearing C bit in TLB miss
handler when the page doesn't have _PAGE_RW flag.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/bbb13848ff0100a76ee9ea95118058c30ae95f2c.1643613343.git.christophe.leroy@csgroup.eu
This commit is contained in:
Christophe Leroy 2022-01-31 07:17:57 +00:00 committed by Michael Ellerman
parent 9872cbfb45
commit 4634bf4455
1 changed files with 2 additions and 0 deletions
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2
arch/powerpc/kernel/head_book3s_32.S
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@ -507,7 +507,9 @@ DataLoadTLBMiss:
/* Convert linux-style PTE to low word of PPC-style PTE */
rlwinm r1,r0,32-9,30,30 /* _PAGE_RW -> PP msb */
rlwimi r0,r0,32-1,30,30 /* _PAGE_USER -> PP msb */
rlwimi r1,r0,32-3,24,24 /* _PAGE_RW -> _PAGE_DIRTY */
rlwimi r0,r0,32-1,31,31 /* _PAGE_USER -> PP lsb */
xori r1,r1,_PAGE_DIRTY /* clear dirty when not rw */
ori r1,r1,0xe04 /* clear out reserved bits */
andc r1,r0,r1 /* PP = user? rw? 1: 3: 0 */
BEGIN_FTR_SECTION