From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
To: linux-kernel@vger.kernel.org, x86@kernel.org,
Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Ravi Shankar <ravi.v.shankar@intel.com>,
Tony Luck <tony.luck@intel.com>,
Sohil Mehta <sohil.mehta@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Subject: [RFC v3 12/12] x86/efi: Disable LASS enforcement when switching to EFI MM
Date: Fri, 9 Jun 2023 21:36:32 +0300 [thread overview]
Message-ID: <20230609183632.48706-13-alexander.shishkin@linux.intel.com> (raw)
In-Reply-To: <20230609183632.48706-1-alexander.shishkin@linux.intel.com>
From: Sohil Mehta <sohil.mehta@intel.com>
[Code is experimental and not yet ready to be merged upstream]
PeterZ suggested that EFI memory can be mapped in user virtual address
space which would trigger LASS violation upon access. It isn't exactly
clear how and when these user address mapping happen. It may be possible
this is related to EFI mixed mode.
Link:https://lore.kernel.org/lkml/Y73S56t%2FwDIGEPlK@hirez.programming.kicks-ass.net/
stac()/clac() calls in the EFI MM enter and exit functions trigger
objtool warnings due to switch_mm() not being classified as
func_uaccess_safe. Refer Objtool warnings section #9 in the document
tools/objtool/Documentation/objtool.txt. This would need to be resolved
before even considering merging.
Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
arch/x86/platform/efi/efi_64.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 232acf418cfb..20966efcd87a 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -473,9 +473,14 @@ void __init efi_dump_pagetable(void)
* while the EFI-mm is borrowed. mmgrab()/mmdrop() is not used because the mm
* can not change under us.
* It should be ensured that there are no concurrent calls to this function.
+ *
+ * Disable LASS enforcement temporarily when switching to EFI MM since it could
+ * be mapped into the low 64-bit virtual address space with address bit 63 set
+ * to 0.
*/
void efi_enter_mm(void)
{
+ stac();
efi_prev_mm = current->active_mm;
current->active_mm = &efi_mm;
switch_mm(efi_prev_mm, &efi_mm, NULL);
@@ -485,6 +490,7 @@ void efi_leave_mm(void)
{
current->active_mm = efi_prev_mm;
switch_mm(&efi_mm, efi_prev_mm, NULL);
+ clac();
}
static DEFINE_SPINLOCK(efi_runtime_lock);
--
2.39.2
next prev parent reply other threads:[~2023-06-09 18:39 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-09 18:36 [PATCH v3 00/12] Enable Linear Address Space Separation support Alexander Shishkin
2023-06-09 18:36 ` [PATCH v3 01/12] x86/cpu: Enumerate the LASS feature bits Alexander Shishkin
2023-06-09 18:36 ` [PATCH v3 02/12] x86/asm: Introduce inline memcpy and memset Alexander Shishkin
2023-06-09 18:36 ` [PATCH v3 03/12] x86/alternatives: Disable LASS when patching kernel alternatives Alexander Shishkin
2023-07-31 22:41 ` Edgecombe, Rick P
2023-08-01 21:10 ` Sohil Mehta
2023-08-01 21:50 ` Edgecombe, Rick P
2023-06-09 18:36 ` [PATCH v3 04/12] x86/cpu: Enable LASS during CPU initialization Alexander Shishkin
2023-06-09 18:36 ` [PATCH v3 05/12] x86/cpu: Remove redundant comment during feature setup Alexander Shishkin
2023-06-09 18:36 ` [PATCH v3 06/12] x86/vsyscall: Reorganize the #PF emulation code Alexander Shishkin
2023-06-09 18:36 ` [PATCH v3 07/12] x86/traps: Consolidate user fixups in exc_general_protection() Alexander Shishkin
2023-06-09 18:36 ` [PATCH v3 08/12] x86/vsyscall: Add vsyscall emulation for #GP Alexander Shishkin
2023-06-09 18:36 ` [PATCH v3 09/12] x86/vsyscall: Disable LASS if vsyscall mode is set to EMULATE Alexander Shishkin
2023-06-09 18:36 ` [PATCH v3 10/12] x86/vsyscall: Document the fact that vsyscall=emulate disables LASS Alexander Shishkin
2023-06-09 18:36 ` [PATCH v3 11/12] x86/cpu: Set LASS CR4 bit as pinning sensitive Alexander Shishkin
2023-06-09 18:36 ` Alexander Shishkin [this message]
2023-07-31 18:00 ` [PATCH v3 00/12] Enable Linear Address Space Separation support Alexander Shishkin
2023-07-31 22:36 ` Edgecombe, Rick P
2023-08-01 19:50 ` Sohil Mehta
2023-08-01 20:38 ` Edgecombe, Rick P
2023-08-04 23:52 ` Edgecombe, Rick P
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