arm64: entry: Allow tramp_alias to access symbols after the 4K boundary

commit 6c5bf79b69f911560fbf82214c0971af6e58e682 upstream.

Systems using kpti enter and exit the kernel through a trampoline mapping
that is always mapped, even when the kernel is not. tramp_valias is a macro
to find the address of a symbol in the trampoline mapping.

Adding extra sets of vectors will expand the size of the entry.tramp.text
section to beyond 4K. tramp_valias will be unable to generate addresses
for symbols beyond 4K as it uses the 12 bit immediate of the add
instruction.

As there are now two registers available when tramp_alias is called,
use the extra register to avoid the 4K limit of the 12 bit immediate.

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CVE-2022-23960
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 67090569815b3676b5c6afddcdaf52b095fc91f2..1057f4c25f077139c340d65d1f15bcfe38e0cb69 100644 (file)
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -103,9 +103,12 @@
 .org .Lventry_start\@ + 128    // Did we overflow the ventry slot?
        .endm
 
-       .macro tramp_alias, dst, sym
+       .macro tramp_alias, dst, sym, tmp
        mov_q   \dst, TRAMP_VALIAS
-       add     \dst, \dst, #(\sym - .entry.tramp.text)
+       adr_l   \tmp, \sym
+       add     \dst, \dst, \tmp
+       adr_l   \tmp, .entry.tramp.text
+       sub     \dst, \dst, \tmp
        .endm
 
        /*
@@ -429,10 +432,10 @@ alternative_else_nop_endif
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
        bne     4f
        msr     far_el1, x29
-       tramp_alias     x30, tramp_exit_native
+       tramp_alias     x30, tramp_exit_native, x29
        br      x30
 4:
-       tramp_alias     x30, tramp_exit_compat
+       tramp_alias     x30, tramp_exit_compat, x29
        br      x30
 #endif
        .else
@@ -998,7 +1001,7 @@ alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0
 alternative_else_nop_endif
 
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
-       tramp_alias     dst=x5, sym=__sdei_asm_exit_trampoline
+       tramp_alias     dst=x5, sym=__sdei_asm_exit_trampoline, tmp=x3
        br      x5
 #endif
 SYM_CODE_END(__sdei_asm_handler)