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Message-ID: <20240731212007.GW26599@noisy.programming.kicks-ass.net>
Date: Wed, 31 Jul 2024 23:20:07 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Guenter Roeck <linux@...ck-us.net>, Jens Axboe <axboe@...nel.dk>,
Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...hat.com>,
Peter Anvin <hpa@...or.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
the arch/x86 maintainers <x86@...nel.org>
Subject: Re: Linux 6.11-rc1
On Wed, Jul 31, 2024 at 07:26:04PM +0200, Thomas Gleixner wrote:
> On Wed, Jul 31 2024 at 18:51, Peter Zijlstra wrote:
> > On Wed, Jul 31, 2024 at 06:31:05PM +0200, Peter Zijlstra wrote:
> > Thomas, this all still relies on the full text section being PMD mapped,
> > and since we don't have ALIGN_ENTRY_TEXT_END and _etext has PAGE_SIZE
> > alignment, can't have a PAGE mapped tail which then doesn't get cloned?
> >
> > Do we want to make pto_clone_entry_text() use PTI_LEVEL_KERNEL_IMAGE
> > such that it will clone whatever it has?
>
> Yes, I think so.
The alternative is ripping that level thing out entirely, and simply
duplicate anything we find in the page-tables.
We could add something like:
WARN_ON_ONCE(IS_ENABLED(CONFIG_X86_64));
in the PTE path, but do we really care?
---
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -47,16 +47,6 @@
#define __GFP_NOTRACK 0
#endif
-/*
- * Define the page-table levels we clone for user-space on 32
- * and 64 bit.
- */
-#ifdef CONFIG_X86_64
-#define PTI_LEVEL_KERNEL_IMAGE PTI_CLONE_PMD
-#else
-#define PTI_LEVEL_KERNEL_IMAGE PTI_CLONE_PTE
-#endif
-
static void __init pti_print_if_insecure(const char *reason)
{
if (boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
@@ -294,14 +284,7 @@ static void __init pti_setup_vsyscall(vo
static void __init pti_setup_vsyscall(void) { }
#endif
-enum pti_clone_level {
- PTI_CLONE_PMD,
- PTI_CLONE_PTE,
-};
-
-static void
-pti_clone_pgtable(unsigned long start, unsigned long end,
- enum pti_clone_level level)
+static void pti_clone_pgtable(unsigned long start, unsigned long end)
{
unsigned long addr;
@@ -341,7 +324,7 @@ pti_clone_pgtable(unsigned long start, u
continue;
}
- if (pmd_leaf(*pmd) || level == PTI_CLONE_PMD) {
+ if (pmd_leaf(*pmd)) {
target_pmd = pti_user_pagetable_walk_pmd(addr);
if (WARN_ON(!target_pmd))
return;
@@ -375,37 +358,33 @@ pti_clone_pgtable(unsigned long start, u
*target_pmd = *pmd;
addr = round_up(addr + 1, PMD_SIZE);
+ continue;
+ }
- } else if (level == PTI_CLONE_PTE) {
-
- /* Walk the page-table down to the pte level */
- pte = pte_offset_kernel(pmd, addr);
- if (pte_none(*pte)) {
- addr = round_up(addr + 1, PAGE_SIZE);
- continue;
- }
-
- /* Only clone present PTEs */
- if (WARN_ON(!(pte_flags(*pte) & _PAGE_PRESENT)))
- return;
+ /* Walk the page-table down to the pte level */
+ pte = pte_offset_kernel(pmd, addr);
+ if (pte_none(*pte)) {
+ addr = round_up(addr + 1, PAGE_SIZE);
+ continue;
+ }
- /* Allocate PTE in the user page-table */
- target_pte = pti_user_pagetable_walk_pte(addr);
- if (WARN_ON(!target_pte))
- return;
+ /* Only clone present PTEs */
+ if (WARN_ON(!(pte_flags(*pte) & _PAGE_PRESENT)))
+ return;
- /* Set GLOBAL bit in both PTEs */
- if (boot_cpu_has(X86_FEATURE_PGE))
- *pte = pte_set_flags(*pte, _PAGE_GLOBAL);
+ /* Allocate PTE in the user page-table */
+ target_pte = pti_user_pagetable_walk_pte(addr);
+ if (WARN_ON(!target_pte))
+ return;
- /* Clone the PTE */
- *target_pte = *pte;
+ /* Set GLOBAL bit in both PTEs */
+ if (boot_cpu_has(X86_FEATURE_PGE))
+ *pte = pte_set_flags(*pte, _PAGE_GLOBAL);
- addr = round_up(addr + 1, PAGE_SIZE);
+ /* Clone the PTE */
+ *target_pte = *pte;
- } else {
- BUG();
- }
+ addr = round_up(addr + 1, PAGE_SIZE);
}
}
@@ -475,7 +454,7 @@ static void __init pti_clone_user_shared
start = CPU_ENTRY_AREA_BASE;
end = start + (PAGE_SIZE * CPU_ENTRY_AREA_PAGES);
- pti_clone_pgtable(start, end, PTI_CLONE_PMD);
+ pti_clone_pgtable(start, end);
}
#endif /* CONFIG_X86_64 */
@@ -495,8 +474,7 @@ static void __init pti_setup_espfix64(vo
static void pti_clone_entry_text(void)
{
pti_clone_pgtable((unsigned long) __entry_text_start,
- (unsigned long) __entry_text_end,
- PTI_CLONE_PMD);
+ (unsigned long) __entry_text_end);
}
/*
@@ -571,7 +549,7 @@ static void pti_clone_kernel_text(void)
* pti_set_kernel_image_nonglobal() did to clear the
* global bit.
*/
- pti_clone_pgtable(start, end_clone, PTI_LEVEL_KERNEL_IMAGE);
+ pti_clone_pgtable(start, end_clone);
/*
* pti_clone_pgtable() will set the global bit in any PMDs
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