There is errata for AMD family 15h CPUs [1] and since
commit dfb09f9b7ab03 ("x86, amd: Avoid cache aliasing penalties on AMD
family 15h") bits [14:12] are being cleared for shared libraries.
Also per-boot ASLR applies over upper bits by OR directly over the
address.As we need special alignment and lower bits values to be set, it makes only a little sense to call get_unmapped_area() after calculating the address. It also can lead to random crashes if get_unmapped_area() actually changes/aligns the address, which we observed on 15h CPU. Usually it's not a problem as there isn't many mappings (except possibly ld.so, uprobes?) and result address is the same before/after get_unmapped_area(). Move align_vdso_addr() after get_unmapped_area() to make sure that errata for AMD 15h is always applied. [1]: https://developer.amd.com/wordpress/media/2012/10/SharedL1InstructionCacheonAMD15hCPU.pdf Cc: Andy Lutomirski <l...@amacapital.net> Cc: Borislav Petkov <b...@alien8.de> Cc: Dmitry Safonov <0x7f454...@gmail.com> Cc: "H. Peter Anvin" <h...@zytor.com> Cc: Ingo Molnar <mi...@redhat.com> Cc: "Kirill A. Shutemov" <kirill.shute...@linux.intel.com> Cc: Thomas Gleixner <t...@linutronix.de> Cc: Vasiliy Khoruzhick <vasil...@arista.com> Cc: x...@kernel.org Signed-off-by: Dmitry Safonov <d...@arista.com> --- arch/x86/entry/vdso/vma.c | 18 ++++++++++-------- arch/x86/include/asm/elf.h | 1 + arch/x86/kernel/sys_x86_64.c | 2 +- 3 files changed, 12 insertions(+), 9 deletions(-) diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c index 5b8b556dbb12..862f0cce3ee6 100644 --- a/arch/x86/entry/vdso/vma.c +++ b/arch/x86/entry/vdso/vma.c @@ -154,18 +154,26 @@ static int map_vdso(const struct vdso_image *image, unsigned long addr) struct mm_struct *mm = current->mm; struct vm_area_struct *vma; unsigned long text_start; + unsigned long area_size = image->size - image->sym_vvar_start; int ret = 0; if (down_write_killable(&mm->mmap_sem)) return -EINTR; - addr = get_unmapped_area(NULL, addr, - image->size - image->sym_vvar_start, 0, 0); + /* Find a bigger place for vma then needed - to align vdso later. */ + area_size += get_align_mask(); + addr = get_unmapped_area(NULL, addr, area_size, 0, 0); if (IS_ERR_VALUE(addr)) { ret = addr; goto up_fail; } + /* + * Forcibly align the final address in case we have a hardware + * issue that requires alignment for performance reasons. + */ + addr = align_vdso_addr(addr); + text_start = addr - image->sym_vvar_start; /* @@ -239,12 +247,6 @@ static unsigned long vdso_addr(unsigned long start, unsigned len) addr = start; } - /* - * Forcibly align the final address in case we have a hardware - * issue that requires alignment for performance reasons. - */ - addr = align_vdso_addr(addr); - return addr; } diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h index 0d157d2a1e2a..88aa49294c9c 100644 --- a/arch/x86/include/asm/elf.h +++ b/arch/x86/include/asm/elf.h @@ -382,4 +382,5 @@ struct va_alignment { extern struct va_alignment va_align; extern unsigned long align_vdso_addr(unsigned long); +extern unsigned long get_align_mask(void); #endif /* _ASM_X86_ELF_H */ diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c index 6a78d4b36a79..4dd74c6f236d 100644 --- a/arch/x86/kernel/sys_x86_64.c +++ b/arch/x86/kernel/sys_x86_64.c @@ -27,7 +27,7 @@ /* * Align a virtual address to avoid aliasing in the I$ on AMD F15h. */ -static unsigned long get_align_mask(void) +unsigned long get_align_mask(void) { /* handle 32- and 64-bit case with a single conditional */ if (va_align.flags < 0 || !(va_align.flags & (2 - mmap_is_ia32()))) -- 2.13.6
