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Groups > linux.kernel > #1241788 > unrolled thread
| Started by | Dave Hansen <dave@sr71.net> |
|---|---|
| First post | 2015-10-07 22:30 +0200 |
| Last post | 2015-10-07 22:50 +0200 |
| Articles | 3 — 2 participants |
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Re: [PATCH 26/26] x86, pkeys: Documentation Dave Hansen <dave@sr71.net> - 2015-10-07 22:30 +0200
Re: [PATCH 26/26] x86, pkeys: Documentation Andy Lutomirski <luto@amacapital.net> - 2015-10-07 22:50 +0200
Re: [PATCH 26/26] x86, pkeys: Documentation Dave Hansen <dave@sr71.net> - 2015-10-07 22:50 +0200
| From | Dave Hansen <dave@sr71.net> |
|---|---|
| Date | 2015-10-07 22:30 +0200 |
| Subject | Re: [PATCH 26/26] x86, pkeys: Documentation |
| Message-ID | <qh3vA-78b-21@gated-at.bofh.it> |
On 10/03/2015 01:17 AM, Ingo Molnar wrote: > Right now the native x86 PTE format allows two protection related bits for > user-space pages: > > _PAGE_BIT_RW: if 0 the page is read-only, if 1 then it's read-write > _PAGE_BIT_NX: if 0 the page is executable, if 1 then it's not executable > > As discussed previously, pkeys allows 'true execute only (--x)' mappings. > > Another possibility would be 'true write-only (-w-)' mappings. How would those work? Protection Keys has a Write-Disable and an Access-Disable bit. But, Access-Disable denies _all_ data access to the region. There's no way to allow only writes. Or am I missing something? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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| From | Andy Lutomirski <luto@amacapital.net> |
|---|---|
| Date | 2015-10-07 22:50 +0200 |
| Message-ID | <qh3OV-7uS-3@gated-at.bofh.it> |
| In reply to | #1241788 |
On Wed, Oct 7, 2015 at 1:24 PM, Dave Hansen <dave@sr71.net> wrote: > On 10/03/2015 01:17 AM, Ingo Molnar wrote: >> Right now the native x86 PTE format allows two protection related bits for >> user-space pages: >> >> _PAGE_BIT_RW: if 0 the page is read-only, if 1 then it's read-write >> _PAGE_BIT_NX: if 0 the page is executable, if 1 then it's not executable >> >> As discussed previously, pkeys allows 'true execute only (--x)' mappings. >> >> Another possibility would be 'true write-only (-w-)' mappings. > > How would those work? > > Protection Keys has a Write-Disable and an Access-Disable bit. But, > Access-Disable denies _all_ data access to the region. There's no way > to allow only writes. Weird. I wonder why Intel did that. I also wonder whether EPT can do write-only. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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| From | Dave Hansen <dave@sr71.net> |
|---|---|
| Date | 2015-10-07 22:50 +0200 |
| Message-ID | <qh3OW-7uS-17@gated-at.bofh.it> |
| In reply to | #1241795 |
On 10/07/2015 01:39 PM, Andy Lutomirski wrote: > On Wed, Oct 7, 2015 at 1:24 PM, Dave Hansen <dave@sr71.net> wrote: >> On 10/03/2015 01:17 AM, Ingo Molnar wrote: >>> Right now the native x86 PTE format allows two protection related bits for >>> user-space pages: >>> >>> _PAGE_BIT_RW: if 0 the page is read-only, if 1 then it's read-write >>> _PAGE_BIT_NX: if 0 the page is executable, if 1 then it's not executable >>> >>> As discussed previously, pkeys allows 'true execute only (--x)' mappings. >>> >>> Another possibility would be 'true write-only (-w-)' mappings. >> >> How would those work? >> >> Protection Keys has a Write-Disable and an Access-Disable bit. But, >> Access-Disable denies _all_ data access to the region. There's no way >> to allow only writes. > > Weird. I wonder why Intel did that. > > I also wonder whether EPT can do write-only. The SDM makes it look that way. There appear to be completely separate r/w/x bits. r=0/w=0/x=0 means !present. The bit 0 definition says, for instance: Read access; indicates whether reads are allowed from the 4-KByte page referenced by this entry -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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