From: Thadeu Lima de Souza Cascardo cascardo@canonical.com
commit 51a6fa0732d6be6a44e0032752ad2ac10d67c796 upstream.
When running with return thunks enabled under 32-bit EFI, the system crashes with:
kernel tried to execute NX-protected page - exploit attempt? (uid: 0) BUG: unable to handle page fault for address: 000000005bc02900 #PF: supervisor instruction fetch in kernel mode #PF: error_code(0x0011) - permissions violation PGD 18f7063 P4D 18f7063 PUD 18ff063 PMD 190e063 PTE 800000005bc02063 Oops: 0011 [#1] PREEMPT SMP PTI CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.19.0-rc6+ #166 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:0x5bc02900 Code: Unable to access opcode bytes at RIP 0x5bc028d6. RSP: 0018:ffffffffb3203e10 EFLAGS: 00010046 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000048 RDX: 000000000190dfac RSI: 0000000000001710 RDI: 000000007eae823b RBP: ffffffffb3203e70 R08: 0000000001970000 R09: ffffffffb3203e28 R10: 747563657865206c R11: 6c6977203a696665 R12: 0000000000001710 R13: 0000000000000030 R14: 0000000001970000 R15: 0000000000000001 FS: 0000000000000000(0000) GS:ffff8e013ca00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0018 ES: 0018 CR0: 0000000080050033 CR2: 000000005bc02900 CR3: 0000000001930000 CR4: 00000000000006f0 Call Trace: ? efi_set_virtual_address_map+0x9c/0x175 efi_enter_virtual_mode+0x4a6/0x53e start_kernel+0x67c/0x71e x86_64_start_reservations+0x24/0x2a x86_64_start_kernel+0xe9/0xf4 secondary_startup_64_no_verify+0xe5/0xeb
That's because it cannot jump to the return thunk from the 32-bit code.
Using a naked RET and marking it as safe allows the system to proceed booting.
Fixes: aa3d480315ba ("x86: Use return-thunk in asm code") Reported-by: Guenter Roeck linux@roeck-us.net Signed-off-by: Thadeu Lima de Souza Cascardo cascardo@canonical.com Cc: Peter Zijlstra (Intel) peterz@infradead.org Cc: Borislav Petkov bp@suse.de Cc: Josh Poimboeuf jpoimboe@kernel.org Cc: stable@vger.kernel.org Tested-by: Guenter Roeck linux@roeck-us.net Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/platform/efi/efi_thunk_64.S | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/arch/x86/platform/efi/efi_thunk_64.S +++ b/arch/x86/platform/efi/efi_thunk_64.S @@ -22,6 +22,7 @@ #include <linux/linkage.h> #include <asm/page_types.h> #include <asm/segment.h> +#include <asm/nospec-branch.h>
.text .code64 @@ -63,7 +64,9 @@ SYM_CODE_START(__efi64_thunk) 1: movq 24(%rsp), %rsp pop %rbx pop %rbp - RET + ANNOTATE_UNRET_SAFE + ret + int3
.code32 2: pushl $__KERNEL_CS