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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-11 08:27:49 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-11 08:27:49 +0000
commitace9429bb58fd418f0c81d4c2835699bddf6bde6 (patch)
treeb2d64bc10158fdd5497876388cd68142ca374ed3 /arch/arm64/kernel/efi-rt-wrapper.S
parentInitial commit. (diff)
downloadlinux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.tar.xz
linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.zip
Adding upstream version 6.6.15.upstream/6.6.15
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'arch/arm64/kernel/efi-rt-wrapper.S')
-rw-r--r--arch/arm64/kernel/efi-rt-wrapper.S87
1 files changed, 87 insertions, 0 deletions
diff --git a/arch/arm64/kernel/efi-rt-wrapper.S b/arch/arm64/kernel/efi-rt-wrapper.S
new file mode 100644
index 0000000000..e8ae803662
--- /dev/null
+++ b/arch/arm64/kernel/efi-rt-wrapper.S
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2018 Linaro Ltd <ard.biesheuvel@linaro.org>
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+SYM_FUNC_START(__efi_rt_asm_wrapper)
+ stp x29, x30, [sp, #-112]!
+ mov x29, sp
+
+ /*
+ * Register x18 is designated as the 'platform' register by the AAPCS,
+ * which means firmware running at the same exception level as the OS
+ * (such as UEFI) should never touch it.
+ */
+ stp x1, x18, [sp, #16]
+
+ /*
+ * Preserve all callee saved registers and preserve the stack pointer
+ * value at the base of the EFI runtime stack so we can recover from
+ * synchronous exceptions occurring while executing the firmware
+ * routines.
+ */
+ stp x19, x20, [sp, #32]
+ stp x21, x22, [sp, #48]
+ stp x23, x24, [sp, #64]
+ stp x25, x26, [sp, #80]
+ stp x27, x28, [sp, #96]
+
+ ldr_l x16, efi_rt_stack_top
+ mov sp, x16
+ stp x18, x29, [sp, #-16]!
+
+ /*
+ * We are lucky enough that no EFI runtime services take more than
+ * 5 arguments, so all are passed in registers rather than via the
+ * stack.
+ */
+ mov x8, x0
+ mov x0, x2
+ mov x1, x3
+ mov x2, x4
+ mov x3, x5
+ mov x4, x6
+ blr x8
+
+ mov x16, sp
+ mov sp, x29
+ str xzr, [x16, #8] // clear recorded task SP value
+
+ ldp x1, x2, [sp, #16]
+ cmp x2, x18
+ ldp x29, x30, [sp], #112
+ b.ne 0f
+ ret
+0:
+ /*
+ * With CONFIG_SHADOW_CALL_STACK, the kernel uses x18 to store a
+ * shadow stack pointer, which we need to restore before returning to
+ * potentially instrumented code. This is safe because the wrapper is
+ * called with preemption disabled and a separate shadow stack is used
+ * for interrupts.
+ */
+#ifdef CONFIG_SHADOW_CALL_STACK
+ ldr_l x18, efi_rt_stack_top
+ ldr x18, [x18, #-16]
+#endif
+
+ b efi_handle_corrupted_x18 // tail call
+SYM_FUNC_END(__efi_rt_asm_wrapper)
+
+SYM_CODE_START(__efi_rt_asm_recover)
+ mov sp, x30
+
+ ldr_l x16, efi_rt_stack_top // clear recorded task SP value
+ str xzr, [x16, #-8]
+
+ ldp x19, x20, [sp, #32]
+ ldp x21, x22, [sp, #48]
+ ldp x23, x24, [sp, #64]
+ ldp x25, x26, [sp, #80]
+ ldp x27, x28, [sp, #96]
+ ldp x29, x30, [sp], #112
+ ret
+SYM_CODE_END(__efi_rt_asm_recover)