Commit-ID: 97193702c6d353e12aefc0fb2f73a98ca421cd56 Gitweb: https://git.kernel.org/tip/97193702c6d353e12aefc0fb2f73a98ca421cd56 Author: Joerg Roedel <jroedel@xxxxxxx> AuthorDate: Wed, 18 Jul 2018 11:41:16 +0200 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitDate: Fri, 20 Jul 2018 01:11:49 +0200 x86/entry/32: Add debug code to check entry/exit CR3 Add code to check whether the kernel is entered and left with the correct CR3 and make it depend on CONFIG_DEBUG_ENTRY. This is needed because there is no NX protection of user-addresses in the kernel-CR3 on x86-32 and that type of bug would not be detected otherwise. Signed-off-by: Joerg Roedel <jroedel@xxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Tested-by: Pavel Machek <pavel@xxxxxx> Cc: "H . Peter Anvin" <hpa@xxxxxxxxx> Cc: linux-mm@xxxxxxxxx Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxx> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Cc: Juergen Gross <jgross@xxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Jiri Kosina <jkosina@xxxxxxx> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> Cc: Brian Gerst <brgerst@xxxxxxxxx> Cc: David Laight <David.Laight@xxxxxxxxxx> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx> Cc: Eduardo Valentin <eduval@xxxxxxxxxx> Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Cc: aliguori@xxxxxxxxxx Cc: daniel.gruss@xxxxxxxxxxxxxx Cc: hughd@xxxxxxxxxx Cc: keescook@xxxxxxxxxx Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Waiman Long <llong@xxxxxxxxxx> Cc: "David H . Gutteridge" <dhgutteridge@xxxxxxxxxxxx> Cc: joro@xxxxxxxxxx Link: https://lkml.kernel.org/r/1531906876-13451-40-git-send-email-joro@xxxxxxxxxx --- arch/x86/entry/entry_32.S | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index b1541c74c71a..010cdb41e3c7 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -166,6 +166,24 @@ .Lend_\@: .endm +.macro BUG_IF_WRONG_CR3 no_user_check=0 +#ifdef CONFIG_DEBUG_ENTRY + ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI + .if \no_user_check == 0 + /* coming from usermode? */ + testl $SEGMENT_RPL_MASK, PT_CS(%esp) + jz .Lend_\@ + .endif + /* On user-cr3? */ + movl %cr3, %eax + testl $PTI_SWITCH_MASK, %eax + jnz .Lend_\@ + /* From userspace with kernel cr3 - BUG */ + ud2 +.Lend_\@: +#endif +.endm + /* * Switch to kernel cr3 if not already loaded and return current cr3 in * \scratch_reg @@ -213,6 +231,8 @@ .macro SAVE_ALL_NMI cr3_reg:req SAVE_ALL + BUG_IF_WRONG_CR3 + /* * Now switch the CR3 when PTI is enabled. * @@ -224,6 +244,7 @@ .Lend_\@: .endm + /* * This is a sneaky trick to help the unwinder find pt_regs on the stack. The * frame pointer is replaced with an encoded pointer to pt_regs. The encoding @@ -287,6 +308,8 @@ .Lswitched_\@: + BUG_IF_WRONG_CR3 + RESTORE_REGS pop=\pop .endm @@ -357,6 +380,8 @@ ALTERNATIVE "", "jmp .Lend_\@", X86_FEATURE_XENPV + BUG_IF_WRONG_CR3 + SWITCH_TO_KERNEL_CR3 scratch_reg=%eax /* @@ -799,6 +824,7 @@ ENTRY(entry_SYSENTER_32) */ pushfl pushl %eax + BUG_IF_WRONG_CR3 no_user_check=1 SWITCH_TO_KERNEL_CR3 scratch_reg=%eax popl %eax popfl @@ -893,6 +919,7 @@ ENTRY(entry_SYSENTER_32) * whereas POPF does not.) */ btrl $X86_EFLAGS_IF_BIT, (%esp) + BUG_IF_WRONG_CR3 no_user_check=1 popfl popl %eax @@ -970,6 +997,8 @@ restore_all: /* Switch back to user CR3 */ SWITCH_TO_USER_CR3 scratch_reg=%eax + BUG_IF_WRONG_CR3 + /* Restore user state */ RESTORE_REGS pop=4 # skip orig_eax/error_code .Lirq_return: @@ -983,6 +1012,7 @@ restore_all: restore_all_kernel: TRACE_IRQS_IRET PARANOID_EXIT_TO_KERNEL_MODE + BUG_IF_WRONG_CR3 RESTORE_REGS 4 jmp .Lirq_return @@ -990,6 +1020,19 @@ restore_all_kernel: ENTRY(iret_exc ) pushl $0 # no error code pushl $do_iret_error + +#ifdef CONFIG_DEBUG_ENTRY + /* + * The stack-frame here is the one that iret faulted on, so its a + * return-to-user frame. We are on kernel-cr3 because we come here from + * the fixup code. This confuses the CR3 checker, so switch to user-cr3 + * as the checker expects it. + */ + pushl %eax + SWITCH_TO_USER_CR3 scratch_reg=%eax + popl %eax +#endif + jmp common_exception .previous _ASM_EXTABLE(.Lirq_return, iret_exc) -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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