Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/2] x86: mm: ptdump: Calculate effective permissions correctly | From | Steven Price <> | Date | Tue, 26 May 2020 11:41:41 +0100 |
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On 22/05/2020 19:07, Qian Cai wrote: > On Thu, May 21, 2020 at 04:23:07PM +0100, Steven Price wrote: >> --- a/arch/x86/mm/dump_pagetables.c >> +++ b/arch/x86/mm/dump_pagetables.c >> @@ -249,10 +249,22 @@ static void note_wx(struct pg_state *st, unsigned long addr) >> @@ -270,16 +282,10 @@ static void note_page(struct ptdump_state *pt_st, unsigned long addr, int level, >> struct seq_file *m = st->seq; >> >> new_prot = val & PTE_FLAGS_MASK; >> + new_eff = st->prot_levels[level]; > > This will trigger, > > .config (if ever matters): > https://raw.githubusercontent.com/cailca/linux-mm/master/x86.config > > [ 104.532621] UBSAN: array-index-out-of-bounds in arch/x86/mm/dump_pagetables.c:284:27 > [ 104.542620] index -1 is out of range for type 'pgprotval_t [5]'
Doh! In this case the result (new_eff) is never actually used: the -1 is used just to flush the last proper entry out, so in this case val == 0 which means the following statement sets new_eff = 0. But obviously an out-of-bounds access isn't great. Thanks for testing!
The following patch should fix it up by making the assignment conditional on val != 0.
Andrew: Would you like me to resend, or can you squash in the below?
Steve
-----8<---- diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c index 17aa7ac94a34..ea9010113f69 100644 --- a/arch/x86/mm/dump_pagetables.c +++ b/arch/x86/mm/dump_pagetables.c @@ -282,10 +282,10 @@ static void note_page(struct ptdump_state *pt_st, unsigned long addr, int level, struct seq_file *m = st->seq;
new_prot = val & PTE_FLAGS_MASK; - new_eff = st->prot_levels[level]; - if (!val) new_eff = 0; + else + new_eff = st->prot_levels[level];
/* * If we have a "break" in the series, we need to flush the state that
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