On Mon, Sep 09 2024 at 05:03, Jamie Heilman wrote:

3db03fb4995e ("x86/mm: Fix pti_clone_entry_text() for i386") which got landed in 6.6.46, has introduced two back to back warnings on boot on my 32bit system (found on 6.6.50):

Right.

Reverting that commit removes the warnings (tested against 6.6.50). The follow-on commit of c48b5a4cf312 ("x86/mm: Fix PTI for i386 some more") doesn't apply cleanly to 6.6.50, but I did try out a build of 6.11-rc7 and that works fine too with no warnings on boot.

See backport below.

Thanks,

tglx --- From: Thomas Gleixner tglx@linutronix.de Date: Tue Aug 6 20:48:43 2024 +0200 Subject: [PATCH 6.6.y, 6.1.y, 5.10.y] x86/mm: Fix PTI for i386 some more

commit c48b5a4cf3125adb679e28ef093f66ff81368d05 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 Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: Guenter Roeck linux@roeck-us.net Link: https://lkml.kernel.org/r/20240806184843.GX37996@noisy.programming.kicks-ass... --- arch/x86/mm/pti.c | 45 +++++++++++++++++++++++++++++---------------- 1 file changed, 29 insertions(+), 16 deletions(-)

--- a/arch/x86/mm/pti.c +++ b/arch/x86/mm/pti.c @@ -241,7 +241,7 @@ static pmd_t *pti_user_pagetable_walk_pm * * 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_pt 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(vo 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, u 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;

@@ -453,7 +458,7 @@ static void __init pti_clone_user_shared 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;

@@ -476,7 +481,7 @@ 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, PTI_CLONE_PMD, false); } #endif /* CONFIG_X86_64 */

@@ -493,11 +498,11 @@ static void __init pti_setup_espfix64(vo /* * 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); }

/* @@ -572,7 +577,7 @@ 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 @@ -639,8 +644,15 @@ 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(); } @@ -657,10 +669,11 @@ 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();