[PATCH] x86/boot/64: Fix missed fixup_pointer() for next_early_pgt access

[PATCH] x86/boot/64: Fix missed fixup_pointer() for next_early_pgt access

[Kirill A. Shutemov]

__startup_64() uses fixup_pointer() to access global variables in a
position-independent fashion. Access to next_early_pgt was wrapped into
the helper, but one of the instance in 5-level paging branch was missed.

GCC generates a R_X86_64_PC32 PC-relative relocation for the access
which doesn't trigger the issue, but Clang emmits a R_X86_64_32S which
leads to an invalid memory and system reboot.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Fixes: 187e91fe5e91 ("x86/boot/64/clang: Use fixup_pointer() to access 'next_early_pgt'")
Cc: Alexander Potapenko <glider@google.com>
---
 arch/x86/kernel/head64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 16b1cbd3a61e..4d98ba8063d1 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -184,7 +184,7 @@ unsigned long __head __startup_64(unsigned long physaddr,
 	pgtable_flags = _KERNPG_TABLE_NOENC + sme_get_me_mask();
 
 	if (la57) {
-		p4d = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);
+		p4d = fixup_pointer(early_dynamic_pgts[(*next_pgt_ptr)++], physaddr);
 
 		i = (physaddr >> PGDIR_SHIFT) % PTRS_PER_PGD;
 		pgd[i + 0] = (pgdval_t)p4d + pgtable_flags;
-- 
2.21.0

[tip:x86/urgent] x86/boot/64: Add missing fixup_pointer() for next_early_pgt access

[tip-bot for Kirill A. Shutemov]

Commit-ID:  c1887159eb48ba40e775584cfb2a443962cf1a05
Gitweb:     https://git.kernel.org/tip/c1887159eb48ba40e775584cfb2a443962cf1a05
Author:     Kirill A. Shutemov <kirill@shutemov.name>
AuthorDate: Thu, 20 Jun 2019 14:24:22 +0300
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 26 Jun 2019 07:25:09 +0200

x86/boot/64: Add missing fixup_pointer() for next_early_pgt access

__startup_64() uses fixup_pointer() to access global variables in a
position-independent fashion. Access to next_early_pgt was wrapped into the
helper, but one instance in the 5-level paging branch was missed.

GCC generates a R_X86_64_PC32 PC-relative relocation for the access which
doesn't trigger the issue, but Clang emmits a R_X86_64_32S which leads to
an invalid memory access and system reboot.

Fixes: 187e91fe5e91 ("x86/boot/64/clang: Use fixup_pointer() to access 'next_early_pgt'")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Alexander Potapenko <glider@google.com>
Link: https://lkml.kernel.org/r/20190620112422.29264-1-kirill.shutemov@linux.intel.com

---
 arch/x86/kernel/head64.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 7df5bce4e1be..29ffa495bd1c 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -184,7 +184,8 @@ unsigned long __head __startup_64(unsigned long physaddr,
 	pgtable_flags = _KERNPG_TABLE_NOENC + sme_get_me_mask();
 
 	if (la57) {
-		p4d = fixup_pointer(early_dynamic_pgts[next_early_pgt++], physaddr);
+		p4d = fixup_pointer(early_dynamic_pgts[(*next_pgt_ptr)++],
+				    physaddr);
 
 		i = (physaddr >> PGDIR_SHIFT) % PTRS_PER_PGD;
 		pgd[i + 0] = (pgdval_t)p4d + pgtable_flags;