| Message ID | 20180508162829.7729-1-glider@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 05/08/2018 09:28 AM, Alexander Potapenko wrote: > Clang builds with defconfig started crashing after commit fb43d6cb91ef > ("x86/mm: Do not auto-massage page protections") > This was caused by introducing a new global access in __startup_64(). > > Code in __startup_64() can be relocated during execution, but the compiler > doesn't have to generate PC-relative relocations when accessing globals > from that function. Clang actually does not generate them, which leads > to boot-time crashes. To work around this problem, every global pointer > must be adjusted using fixup_pointer(). Looks good to me. Thanks for adding the comment, especially! Reviewed-by: Dave Hansen <dave.hansen@intel.com>
On Tue, May 08, 2018 at 04:28:29PM +0000, Alexander Potapenko wrote: > @@ -196,7 +204,8 @@ unsigned long __head __startup_64(unsigned long physaddr, > > pmd_entry = __PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL; > /* Filter out unsupported __PAGE_KERNEL_* bits: */ > - pmd_entry &= __supported_pte_mask; > + mask_ptr = (pteval_t *)fixup_pointer(&__supported_pte_mask, physaddr); Do we really need the cast here?
On Tue, May 8, 2018 at 11:44 PM Kirill A. Shutemov < kirill.shutemov@linux.intel.com> wrote: > On Tue, May 08, 2018 at 04:28:29PM +0000, Alexander Potapenko wrote: > > @@ -196,7 +204,8 @@ unsigned long __head __startup_64(unsigned long physaddr, > > > > pmd_entry = __PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL; > > /* Filter out unsupported __PAGE_KERNEL_* bits: */ > > - pmd_entry &= __supported_pte_mask; > > + mask_ptr = (pteval_t *)fixup_pointer(&__supported_pte_mask, physaddr); > Do we really need the cast here? Correct, we do not. > -- > Kirill A. Shutemov
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c index 0c408f8c4ed4..9223792f6d0e 100644 --- a/arch/x86/kernel/head64.c +++ b/arch/x86/kernel/head64.c @@ -104,6 +104,13 @@ static bool __head check_la57_support(unsigned long physaddr) } #endif + +/* Code in __startup_64() can be relocated during execution, but the compiler + * doesn't have to generate PC-relative relocations when accessing globals from + * that function. Clang actually does not generate them, which leads to + * boot-time crashes. To work around this problem, every global pointer must + * be adjusted using fixup_pointer(). + */ unsigned long __head __startup_64(unsigned long physaddr, struct boot_params *bp) { @@ -113,6 +120,7 @@ unsigned long __head __startup_64(unsigned long physaddr, p4dval_t *p4d; pudval_t *pud; pmdval_t *pmd, pmd_entry; + pteval_t *mask_ptr; bool la57; int i; unsigned int *next_pgt_ptr; @@ -196,7 +204,8 @@ unsigned long __head __startup_64(unsigned long physaddr, pmd_entry = __PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL; /* Filter out unsupported __PAGE_KERNEL_* bits: */ - pmd_entry &= __supported_pte_mask; + mask_ptr = (pteval_t *)fixup_pointer(&__supported_pte_mask, physaddr); + pmd_entry &= *mask_ptr; pmd_entry += sme_get_me_mask(); pmd_entry += physaddr;
Clang builds with defconfig started crashing after commit fb43d6cb91ef ("x86/mm: Do not auto-massage page protections") This was caused by introducing a new global access in __startup_64(). Code in __startup_64() can be relocated during execution, but the compiler doesn't have to generate PC-relative relocations when accessing globals from that function. Clang actually does not generate them, which leads to boot-time crashes. To work around this problem, every global pointer must be adjusted using fixup_pointer(). Signed-off-by: Alexander Potapenko <glider@google.com> Fixes: fb43d6cb91ef ("x86/mm: Do not auto-massage page protections") --- v2: better patch description, added a comment to __startup_64() --- arch/x86/kernel/head64.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)