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[v3,06/14] x86: Physical address comparisons in fill_p*d/pte

Message ID 926742095b7e55099cc48d70848ca3c1eff4b5eb.1743772053.git.maciej.wieczor-retman@intel.com (mailing list archive)
State New
Headers show
Series [v3,01/14] kasan: sw_tags: Use arithmetic shift for shadow computation | expand

Commit Message

Maciej Wieczor-Retman April 4, 2025, 1:14 p.m. UTC 
Calculating page offset returns a pointer without a tag. When comparing
the calculated offset to a tagged page pointer an error is raised
because they are not equal.

Change pointer comparisons to physical address comparisons as to avoid
issues with tagged pointers that pointer arithmetic would create. Open
code pte_offset_kernel(), pmd_offset(), pud_offset() and p4d_offset().
Because one parameter is always zero and the rest of the function
insides are enclosed inside __va(), removing that layer lowers the
complexity of final assembly.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
---
Changelog v2:
- Open code *_offset() to avoid it's internal __va().

 arch/x86/mm/init_64.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

Comments

Dave Hansen April 4, 2025, 4:56 p.m. UTC | #1 
On 4/4/25 06:14, Maciej Wieczor-Retman wrote:
> +		if (__pa(p4d) != (pgtable_l5_enabled() ?
> +				  (unsigned long)pgd_val(*pgd) & PTE_PFN_MASK :
> +				  __pa(pgd)))
>  			printk(KERN_ERR "PAGETABLE BUG #00! %p <-> %p\n",

This one is pretty fugly. But I guess it's just one place and it
probably isn't worth refactoring this and the other helpers just for a
debug message.
diff mbox series

Patch

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 519aa53114fa..d40699c16f14 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -251,7 +251,10 @@  static p4d_t *fill_p4d(pgd_t *pgd, unsigned long vaddr)
 	if (pgd_none(*pgd)) {
 		p4d_t *p4d = (p4d_t *)spp_getpage();
 		pgd_populate(&init_mm, pgd, p4d);
-		if (p4d != p4d_offset(pgd, 0))
+
+		if (__pa(p4d) != (pgtable_l5_enabled() ?
+				  (unsigned long)pgd_val(*pgd) & PTE_PFN_MASK :
+				  __pa(pgd)))
 			printk(KERN_ERR "PAGETABLE BUG #00! %p <-> %p\n",
 			       p4d, p4d_offset(pgd, 0));
 	}
@@ -263,7 +266,7 @@  static pud_t *fill_pud(p4d_t *p4d, unsigned long vaddr)
 	if (p4d_none(*p4d)) {
 		pud_t *pud = (pud_t *)spp_getpage();
 		p4d_populate(&init_mm, p4d, pud);
-		if (pud != pud_offset(p4d, 0))
+		if (__pa(pud) != (p4d_val(*p4d) & p4d_pfn_mask(*p4d)))
 			printk(KERN_ERR "PAGETABLE BUG #01! %p <-> %p\n",
 			       pud, pud_offset(p4d, 0));
 	}
@@ -275,7 +278,7 @@  static pmd_t *fill_pmd(pud_t *pud, unsigned long vaddr)
 	if (pud_none(*pud)) {
 		pmd_t *pmd = (pmd_t *) spp_getpage();
 		pud_populate(&init_mm, pud, pmd);
-		if (pmd != pmd_offset(pud, 0))
+		if (__pa(pmd) != (pud_val(*pud) & pud_pfn_mask(*pud)))
 			printk(KERN_ERR "PAGETABLE BUG #02! %p <-> %p\n",
 			       pmd, pmd_offset(pud, 0));
 	}
@@ -287,7 +290,7 @@  static pte_t *fill_pte(pmd_t *pmd, unsigned long vaddr)
 	if (pmd_none(*pmd)) {
 		pte_t *pte = (pte_t *) spp_getpage();
 		pmd_populate_kernel(&init_mm, pmd, pte);
-		if (pte != pte_offset_kernel(pmd, 0))
+		if (__pa(pte) != (pmd_val(*pmd) & pmd_pfn_mask(*pmd)))
 			printk(KERN_ERR "PAGETABLE BUG #03!\n");
 	}
 	return pte_offset_kernel(pmd, vaddr);