Messages in this thread | | | Subject | Re: [PATCH v1 1/5] powerpc/mm: sanity_check_fault() should work for all, not only BOOK3S | From | Christophe Leroy <> | Date | Tue, 8 Sep 2020 10:56:29 +0200 |
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Le 08/09/2020 à 10:43, Nicholas Piggin a écrit : > Excerpts from Christophe Leroy's message of August 7, 2020 3:15 am: >> The verification and message introduced by commit 374f3f5979f9 >> ("powerpc/mm/hash: Handle user access of kernel address gracefully") >> applies to all platforms, it should not be limited to BOOK3S. >> >> Make the BOOK3S version of sanity_check_fault() the one for all, >> and bail out earlier if not BOOK3S. >> >> Fixes: 374f3f5979f9 ("powerpc/mm/hash: Handle user access of kernel address gracefully") >> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> >> --- >> arch/powerpc/mm/fault.c | 8 +++----- >> 1 file changed, 3 insertions(+), 5 deletions(-) >> >> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c >> index 925a7231abb3..2efa34d7e644 100644 >> --- a/arch/powerpc/mm/fault.c >> +++ b/arch/powerpc/mm/fault.c >> @@ -303,7 +303,6 @@ static inline void cmo_account_page_fault(void) >> static inline void cmo_account_page_fault(void) { } >> #endif /* CONFIG_PPC_SMLPAR */ >> >> -#ifdef CONFIG_PPC_BOOK3S >> static void sanity_check_fault(bool is_write, bool is_user, >> unsigned long error_code, unsigned long address) >> { >> @@ -320,6 +319,9 @@ static void sanity_check_fault(bool is_write, bool is_user, >> return; >> } >> >> + if (!IS_ENABLED(CONFIG_PPC_BOOK3S)) >> + return; > > Seems okay. Why is address == -1 special though? I guess it's because > it may not be an exploit kernel reference but a buggy pointer underflow? > In that case -1 doesn't seem like it would catch very much. Would it be > better to test for high bit set for example ((long)address < 0) ?
See https://github.com/linuxppc/linux/commit/0f9aee0cb9da7db7d96f63cfa2dc5e4f1bffeb87#diff-f9658f412252f3bb3093e0a95b37f3ac
-1 is what mmap() returns on error, if the app uses that as a pointer that's a programming error not an exploit.
Euh .. If you test (long)address < 0, then the entire kernel falls into that range as usually it goes from 0xc0000000 to 0xffffffff
But we could skip the top page entirely, anyway it is never mapped.
> > Anyway for your patch > > Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Thanks Christophe
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