On 8/6/24 11:48, Peter Zijlstra wrote:
On Tue, Aug 06, 2024 at 09:42:23AM -0700, Guenter Roeck wrote:On 8/6/24 08:59, Peter Zijlstra wrote:On Tue, Aug 06, 2024 at 05:46:53PM +0200, Peter Zijlstra wrote:On Tue, Aug 06, 2024 at 05:05:15PM +0200, Peter Zijlstra wrote:On Tue, Aug 06, 2024 at 04:56:32PM +0200, Peter Zijlstra wrote:On Tue, Aug 06, 2024 at 07:25:42AM -0700, Guenter Roeck wrote:I created http://server.roeck-us.net/qemu/x86-v6.11-rc2/ with all the relevant information. Please let me know if you need anything else.So I grabbed that config, stuck it in the build dir I used last time and upgraded gcc-13 from 13.2 ro 13.3. But alas, my build runs successfully :/ Is there anything else special I missed?run.sh is not exacrlty the same this time, different CPU model, that made it go. OK, lemme poke at this.Urgh, so crypto's late_initcall() does user-mode-helper based modprobe looking for algorithms before we kick off /bin/init :/ This makes things difficult. Urgh.So the problem is that mark_readonly() splits a code PMD due to NX. Then the second pti_clone_entry_text() finds a kernel PTE but a user PMD mapping for the same address (from the early clone) and gets upset. And we can't run mark_readonly() sooner, because initcall expect stuff to be RW. But initcalls do modprobe, which runs user crap before we're done initializing everything. This is a right mess, and I really don't know what to do.And there was me thinking this one should be easy to solve. Oh well. Maybe Linus has an idea ? I am getting a bit wary to reporting all those weird problems to him, though.While I had dinner with the family, Thomas cooked up the below, which seems to make it happy.
I'll give it a try for all emulations (both x86 and x86_64), just to be sure, but it does indeed fix the problem for the test with the affected CPU/build. Thanks! Guenter
It basically splits the PMD on the late copy. --- diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c index bfdf5f45b137..b6ebbc9c23b1 100644 --- a/arch/x86/mm/pti.c +++ b/arch/x86/mm/pti.c @@ -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_leaf(*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 voidpti_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 @@ -639,7 +644,7 @@ 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(); + pti_clone_entry_text(false); pti_setup_espfix64(); pti_setup_vsyscall(); } @@ -659,7 +664,7 @@ void pti_finalize(void) * We need to clone everything (again) that maps parts of the * kernel image. */ - pti_clone_entry_text(); + pti_clone_entry_text(true); pti_clone_kernel_text();debug_checkwx_user();
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