Messages in this thread | | | From | Dexuan Cui <> | Subject | RE: hv_hypercall_pg page permissios | Date | Mon, 15 Jun 2020 19:49:41 +0000 |
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> From: linux-hyperv-owner@vger.kernel.org > <linux-hyperv-owner@vger.kernel.org> On Behalf Of Dexuan Cui > Sent: Monday, June 15, 2020 10:42 AM > > > > > > Hi hch, > > > The patch is merged into the mainine recently, but unluckily we noticed > > > a warning with CONFIG_DEBUG_WX=y > > > > > > Should we revert this patch, or figure out a way to ask the DEBUG_WX > > > code to ignore this page? > > > > Are you sure it is hv_hypercall_pg? > Yes, 100% sure. I printed the value of hv_hypercall_pg and and it matched the > address in the warning line " x86/mm: Found insecure W+X mapping at > address".
I did this experiment: 1. export vmalloc_exec and ptdump_walk_pgd_level_checkwx. 2. write a test module that calls them. 3. It turns out that every call of vmalloc_exec() triggers such a warning.
vmalloc_exec() uses PAGE_KERNEL_EXEC, which is defined as (__PP|__RW| 0|___A| 0|___D| 0|___G)
It looks the logic in note_page() is: for_each_RW_page, if the NX bit is unset, then report the page as an insecure W+X mapping. IMO this explains the warning?
Thanks, -- Dexuan
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