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x86/mm: Fix PTI for i386 some more

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commit c48b5a4cf3 upstream.

So it turns out that we have to do two passes of
pti_clone_entry_text(), once before initcalls, such that device and
late initcalls can use user-mode-helper / modprobe and once after
free_initmem() / mark_readonly().

Now obviously mark_readonly() can cause PMD splits, and
pti_clone_pgtable() doesn't like that much.

Allow the late clone to split PMDs so that pagetables stay in sync.

[peterz: Changelog and comments]
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lkml.kernel.org/r/20240806184843.GX37996@noisy.programming.kicks-ass.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Thomas Gleixner 2024-08-06 20:48:43 +02:00 committed by Greg Kroah-Hartman
parent 413e785a89
commit ba2af6448f
1 changed files with 29 additions and 16 deletions
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45
arch/x86/mm/pti.c
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@ -241,7 +241,7 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
*
* Returns a pointer to a PTE on success, or NULL on failure.
*/
static pte_t *pti_user_pagetable_walk_pte(unsigned long address)
static pte_t *pti_user_pagetable_walk_pte(unsigned long address, bool late_text)
{
gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
pmd_t *pmd;
@ -251,10 +251,15 @@ static pte_t *pti_user_pagetable_walk_pte(unsigned long address)
if (!pmd)
return NULL;
/* We can't do anything sensible if we hit a large mapping. */
/* Large PMD mapping found */
if (pmd_large(*pmd)) {
WARN_ON(1);
return NULL;
/* Clear the PMD if we hit a large mapping from the first round */
if (late_text) {
set_pmd(pmd, __pmd(0));
} else {
WARN_ON_ONCE(1);
return NULL;
}
}
if (pmd_none(*pmd)) {
@ -283,7 +288,7 @@ static void __init pti_setup_vsyscall(void)
if (!pte || WARN_ON(level != PG_LEVEL_4K) || pte_none(*pte))
return;
target_pte = pti_user_pagetable_walk_pte(VSYSCALL_ADDR);
target_pte = pti_user_pagetable_walk_pte(VSYSCALL_ADDR, false);
if (WARN_ON(!target_pte))
return;
@ -301,7 +306,7 @@ enum pti_clone_level {
static void
pti_clone_pgtable(unsigned long start, unsigned long end,
enum pti_clone_level level)
enum pti_clone_level level, bool late_text)
{
unsigned long addr;
@ -390,7 +395,7 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
return;
/* Allocate PTE in the user page-table */
target_pte = pti_user_pagetable_walk_pte(addr);
target_pte = pti_user_pagetable_walk_pte(addr, late_text);
if (WARN_ON(!target_pte))
return;
@ -452,7 +457,7 @@ static void __init pti_clone_user_shared(void)
phys_addr_t pa = per_cpu_ptr_to_phys((void *)va);
pte_t *target_pte;
target_pte = pti_user_pagetable_walk_pte(va);
target_pte = pti_user_pagetable_walk_pte(va, false);
if (WARN_ON(!target_pte))
return;
@ -475,7 +480,7 @@ static void __init pti_clone_user_shared(void)
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, PTI_CLONE_PMD, false);
}
#endif /* CONFIG_X86_64 */
@ -492,11 +497,11 @@ static void __init pti_setup_espfix64(void)
/*
* Clone the populated PMDs of the entry text and force it RO.
*/
static void pti_clone_entry_text(void)
static void pti_clone_entry_text(bool late)
{
pti_clone_pgtable((unsigned long) __entry_text_start,
(unsigned long) __entry_text_end,
PTI_LEVEL_KERNEL_IMAGE);
PTI_LEVEL_KERNEL_IMAGE, late);
}
/*
@ -571,7 +576,7 @@ 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_LEVEL_KERNEL_IMAGE, false);
/*
* pti_clone_pgtable() will set the global bit in any PMDs
@ -638,8 +643,15 @@ void __init pti_init(void)
/* Undo all global bits from the init pagetables in head_64.S: */
pti_set_kernel_image_nonglobal();
/* Replace some of the global bits just for shared entry text: */
pti_clone_entry_text();
/*
* This is very early in boot. Device and Late initcalls can do
* modprobe before free_initmem() and mark_readonly(). This
* pti_clone_entry_text() allows those user-mode-helpers to function,
* but notably the text is still RW.
*/
pti_clone_entry_text(false);
pti_setup_espfix64();
pti_setup_vsyscall();
}
@ -656,10 +668,11 @@ void pti_finalize(void)
if (!boot_cpu_has(X86_FEATURE_PTI))
return;
/*
* We need to clone everything (again) that maps parts of the
* kernel image.
* This is after free_initmem() (all initcalls are done) and we've done
* mark_readonly(). Text is now NX which might've split some PMDs
* relative to the early clone.
*/
pti_clone_entry_text();
pti_clone_entry_text(true);
pti_clone_kernel_text();
debug_checkwx_user();