Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1291489

[PATCH 19/32] x86, pkeys: optimize fault handling in access_error()

Show all headers | View raw

From: Dave Hansen <dave.hansen@linux.intel.com>

We might not strictly have to make modifictions to
access_error() to check the VMA here.

If we do not, we will do this:
1. app sets VMA pkey to K
2. app touches a !present page
3. do_page_fault(), allocates and maps page, sets pte.pkey=K
4. return to userspace
5. touch instruction reexecutes, but triggers PF_PK
6. do PKEY signal

What happens with this patch applied:
1. app sets VMA pkey to K
2. app touches a !present page
3. do_page_fault() notices that K is inaccessible
4. do PKEY signal

We basically skip the fault that does an allocation.

So what this lets us do is protect areas from even being
*populated* unless it is accessible according to protection
keys.  That seems handy to me and makes protection keys work
more like an mprotect()'d mapping.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
---

 b/arch/x86/mm/fault.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff -puN arch/x86/mm/fault.c~pkeys-15-access_error arch/x86/mm/fault.c
--- a/arch/x86/mm/fault.c~pkeys-15-access_error	2015-12-14 10:42:47.386008400 -0800
+++ b/arch/x86/mm/fault.c	2015-12-14 10:42:47.390008579 -0800
@@ -900,10 +900,16 @@ bad_area(struct pt_regs *regs, unsigned
 static inline bool bad_area_access_from_pkeys(unsigned long error_code,
 		struct vm_area_struct *vma)
 {
+	/* This code is always called on the current mm */
+	bool foreign = false;
+
 	if (!boot_cpu_has(X86_FEATURE_OSPKE))
 		return false;
 	if (error_code & PF_PK)
 		return true;
+	/* this checks permission keys on the VMA: */
+	if (!arch_vma_access_permitted(vma, (error_code & PF_WRITE), foreign))
+		return true;
 	return false;
 }
 
@@ -1091,6 +1097,8 @@ int show_unhandled_signals = 1;
 static inline int
 access_error(unsigned long error_code, struct vm_area_struct *vma)
 {
+	/* This is only called for the current mm, so: */
+	bool foreign = false;
 	/*
 	 * Access or read was blocked by protection keys. We do
 	 * this check before any others because we do not want
@@ -1099,6 +1107,13 @@ access_error(unsigned long error_code, s
 	 */
 	if (error_code & PF_PK)
 		return 1;
+	/*
+	 * Make sure to check the VMA so that we do not perform
+	 * faults just to hit a PF_PK as soon as we fill in a
+	 * page.
+	 */
+	if (!arch_vma_access_permitted(vma, (error_code & PF_WRITE), foreign))
+		return 1;
 
 	if (error_code & PF_WRITE) {
 		/* write, present and write, not present: */
_
--
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/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 00/32] x86: Memory Protection Keys (v7) Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
  [PATCH 06/32] x86, pkeys: add PKRU xsave fields and data structure(s) Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
  [PATCH 17/32] x86, pkeys: check VMAs and PTEs for protection keys Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
  [PATCH 14/32] x86, pkeys: add functions to fetch PKRU Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
    Re: [PATCH 14/32] x86, pkeys: add functions to fetch PKRU Thomas Gleixner <tglx@linutronix.de> - 2015-12-14 21:00 +0100
  [PATCH 19/32] x86, pkeys: optimize fault handling in access_error() Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
  [PATCH 10/32] x86, pkeys: arch-specific protection bits Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
  [PATCH 13/32] x86, pkeys: fill in pkey field in siginfo Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
  [PATCH 20/32] x86, pkeys: differentiate instruction fetches Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
  [PATCH 05/32] x86, pkeys: define new CR4 bit Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
  [PATCH 01/32] mm, gup: introduce concept of "foreign" get_user_pages() Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
  [PATCH 08/32] x86, pkeys: new page fault error code bit: PF_PK Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
  [PATCH 11/32] x86, pkeys: pass VMA down in to fault signal generation code Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
  [PATCH 23/32] x86, pkeys: add Kconfig prompt to existing config option Dave Hansen <dave@sr71.net> - 2015-12-14 20:20 +0100
  Re: [PATCH 00/32] x86: Memory Protection Keys (v7) "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2015-12-24 12:40 +0100

csiph-web