__startup_64() is normally using fixup_pointer() to access globals in a
position-independent fashion. However |next_early_pgt| was accessed
directly, which wasn't guaranteed to work.
Luckily GCC was generating a R_X86_64_PC32 PC-relative relocation for
|next_early_pgt|, but Clang emitted a R_X86_64_32S, which led to
accessing invalid memory and rebooting the kernel.
Cc: Kirill A. Shutemov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Michael Davidson <[email protected]>
Fixes: c88d71508e36 ("x86/boot/64: Rewrite startup_64() in C")
Signed-off-by: Alexander Potapenko <[email protected]>
---
arch/x86/kernel/head64.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 46c3c73e7f43..9ba79543d9ee 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -53,6 +53,7 @@ void __head __startup_64(unsigned long physaddr)
pudval_t *pud;
pmdval_t *pmd, pmd_entry;
int i;
+ unsigned int *next_pgt_ptr;
/* Is the address too large? */
if (physaddr >> MAX_PHYSMEM_BITS)
@@ -91,9 +92,9 @@ void __head __startup_64(unsigned long physaddr)
* creates a bunch of nonsense entries but that is fine --
* it avoids problems around wraparound.
*/
-
- pud = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);
- pmd = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);
+ next_pgt_ptr = fixup_pointer(&next_early_pgt, physaddr);
+ pud = fixup_pointer(early_dynamic_pgts[(*next_pgt_ptr)++], physaddr);
+ pmd = fixup_pointer(early_dynamic_pgts[(*next_pgt_ptr)++], physaddr);
if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
p4d = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);
--
2.14.1.480.gb18f417b89-goog
On Wed, Aug 16, 2017 at 9:08 PM, Alexander Potapenko <[email protected]> wrote:
> __startup_64() is normally using fixup_pointer() to access globals in a
> position-independent fashion. However |next_early_pgt| was accessed
> directly, which wasn't guaranteed to work.
>
> Luckily GCC was generating a R_X86_64_PC32 PC-relative relocation for
> |next_early_pgt|, but Clang emitted a R_X86_64_32S, which led to
> accessing invalid memory and rebooting the kernel.
>
> Cc: Kirill A. Shutemov <[email protected]>
> Cc: Dmitry Vyukov <[email protected]>
> Cc: Michael Davidson <[email protected]>
> Fixes: c88d71508e36 ("x86/boot/64: Rewrite startup_64() in C")
> Signed-off-by: Alexander Potapenko <[email protected]>
> ---
> arch/x86/kernel/head64.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 46c3c73e7f43..9ba79543d9ee 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -53,6 +53,7 @@ void __head __startup_64(unsigned long physaddr)
> pudval_t *pud;
> pmdval_t *pmd, pmd_entry;
> int i;
> + unsigned int *next_pgt_ptr;
>
> /* Is the address too large? */
> if (physaddr >> MAX_PHYSMEM_BITS)
> @@ -91,9 +92,9 @@ void __head __startup_64(unsigned long physaddr)
> * creates a bunch of nonsense entries but that is fine --
> * it avoids problems around wraparound.
> */
> -
> - pud = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);
> - pmd = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);
> + next_pgt_ptr = fixup_pointer(&next_early_pgt, physaddr);
> + pud = fixup_pointer(early_dynamic_pgts[(*next_pgt_ptr)++], physaddr);
> + pmd = fixup_pointer(early_dynamic_pgts[(*next_pgt_ptr)++], physaddr);
>
> if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
> p4d = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);
> --
> 2.14.1.480.gb18f417b89-goog
>
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
On Wed, Aug 16, 2017 at 09:08:08PM +0200, Alexander Potapenko wrote:
> __startup_64() is normally using fixup_pointer() to access globals in a
> position-independent fashion. However |next_early_pgt| was accessed
> directly, which wasn't guaranteed to work.
>
> Luckily GCC was generating a R_X86_64_PC32 PC-relative relocation for
> |next_early_pgt|, but Clang emitted a R_X86_64_32S, which led to
> accessing invalid memory and rebooting the kernel.
Thanks for tracking this down.
Acked-by: Kirill A. Shutemov <[email protected]>
> Cc: Kirill A. Shutemov <[email protected]>
> Cc: Dmitry Vyukov <[email protected]>
> Cc: Michael Davidson <[email protected]>
> Fixes: c88d71508e36 ("x86/boot/64: Rewrite startup_64() in C")
Cc: <[email protected]> # 4.12
--
Kirill A. Shutemov
Commit-ID: 187e91fe5e915f4b7f39b824aa422493463e443d
Gitweb: http://git.kernel.org/tip/187e91fe5e915f4b7f39b824aa422493463e443d
Author: Alexander Potapenko <[email protected]>
AuthorDate: Wed, 16 Aug 2017 21:08:08 +0200
Committer: Ingo Molnar <[email protected]>
CommitDate: Thu, 17 Aug 2017 09:53:00 +0200
x86/boot/64/clang: Use fixup_pointer() to access 'next_early_pgt'
__startup_64() is normally using fixup_pointer() to access globals in a
position-independent fashion. However 'next_early_pgt' was accessed
directly, which wasn't guaranteed to work.
Luckily GCC was generating a R_X86_64_PC32 PC-relative relocation for
'next_early_pgt', but Clang emitted a R_X86_64_32S, which led to
accessing invalid memory and rebooting the kernel.
Signed-off-by: Alexander Potapenko <[email protected]>
Acked-by: Kirill A. Shutemov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Michael Davidson <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: c88d71508e36 ("x86/boot/64: Rewrite startup_64() in C")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/kernel/head64.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 46c3c73..9ba7954 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -53,6 +53,7 @@ void __head __startup_64(unsigned long physaddr)
pudval_t *pud;
pmdval_t *pmd, pmd_entry;
int i;
+ unsigned int *next_pgt_ptr;
/* Is the address too large? */
if (physaddr >> MAX_PHYSMEM_BITS)
@@ -91,9 +92,9 @@ void __head __startup_64(unsigned long physaddr)
* creates a bunch of nonsense entries but that is fine --
* it avoids problems around wraparound.
*/
-
- pud = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);
- pmd = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);
+ next_pgt_ptr = fixup_pointer(&next_early_pgt, physaddr);
+ pud = fixup_pointer(early_dynamic_pgts[(*next_pgt_ptr)++], physaddr);
+ pmd = fixup_pointer(early_dynamic_pgts[(*next_pgt_ptr)++], physaddr);
if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
p4d = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);