From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
Catalin Marinas <catalin.marinas@arm.com>,
Marc Zyngier <marc.zyngier@arm.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Christoffer Dall <christoffer.dall@linaro.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Laura Abbott <labbott@redhat.com>
Subject: Re: [PATCH v2 01/11] arm64: use RET instruction for exiting the trampoline
Date: Sat, 6 Jan 2018 13:13:23 +0000 [thread overview]
Message-ID: <CAKv+Gu-efng1k+QbeKmd2pGz1p4vhoFE4fZ8rZ7bihGvsb-e+w@mail.gmail.com> (raw)
In-Reply-To: <1515157961-20963-2-git-send-email-will.deacon@arm.com>
On 5 January 2018 at 13:12, Will Deacon <will.deacon@arm.com> wrote:
> Speculation attacks against the entry trampoline can potentially resteer
> the speculative instruction stream through the indirect branch and into
> arbitrary gadgets within the kernel.
>
> This patch defends against these attacks by forcing a misprediction
> through the return stack: a dummy BL instruction loads an entry into
> the stack, so that the predicted program flow of the subsequent RET
> instruction is to a branch-to-self instruction which is finally resolved
> as a branch to the kernel vectors with speculation suppressed.
>
How safe is it to assume that every microarchitecture will behave as
expected here? Wouldn't it be safer in general not to rely on a memory
load for x30 in the first place? (see below) Or may the speculative
execution still branch anywhere even if the branch target is
guaranteed to be known by that time?
> Signed-off-by: Will Deacon <will.deacon@arm.com>
> ---
> arch/arm64/kernel/entry.S | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 031392ee5f47..71092ee09b6b 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -1029,6 +1029,14 @@ alternative_else_nop_endif
> .if \regsize == 64
> msr tpidrro_el0, x30 // Restored in kernel_ventry
> .endif
> + /*
> + * Defend against branch aliasing attacks by pushing a dummy
> + * entry onto the return stack and using a RET instruction to
> + * entr the full-fat kernel vectors.
> + */
> + bl 2f
> + b .
> +2:
> tramp_map_kernel x30
> #ifdef CONFIG_RANDOMIZE_BASE
> adr x30, tramp_vectors + PAGE_SIZE
> @@ -1041,7 +1049,7 @@ alternative_insn isb, nop, ARM64_WORKAROUND_QCOM_FALKOR_E1003
> msr vbar_el1, x30
> add x30, x30, #(1b - tramp_vectors)
> isb
> - br x30
> + ret
> .endm
>
> .macro tramp_exit, regsize = 64
> --
> 2.1.4
>
This uses Marc's callback alternative patching for the KASLR case, the
non-KASLR case just uses a plain movz/movk sequence to load the
address of vectors rather than a literal.
(apologies for the patch soup)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 55d05dacd02e..e8a846335e8e 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -1031,17 +1031,19 @@ alternative_else_nop_endif
.endif
tramp_map_kernel x30
#ifdef CONFIG_RANDOMIZE_BASE
- adr x30, tramp_vectors + PAGE_SIZE
alternative_insn isb, nop, ARM64_WORKAROUND_QCOM_FALKOR_E1003
- ldr x30, [x30]
+ b tramp_vectors + PAGE_SIZE + .Ltramp_stage2_size * (1b
- tramp_vectors - 0x400) / 0x80
#else
- ldr x30, =vectors
-#endif
+ movz x30, :abs_g3:vectors
+ movk x30, :abs_g2_nc:vectors
+ movk x30, :abs_g1_nc:vectors
+ movk x30, :abs_g0_nc:vectors
prfm plil1strm, [x30, #(1b - tramp_vectors)]
msr vbar_el1, x30
add x30, x30, #(1b - tramp_vectors)
isb
br x30
+#endif
.endm
.macro tramp_exit, regsize = 64
@@ -1080,12 +1082,25 @@ END(tramp_exit_compat)
.ltorg
.popsection // .entry.tramp.text
#ifdef CONFIG_RANDOMIZE_BASE
- .pushsection ".rodata", "a"
+ .pushsection ".text", "ax"
.align PAGE_SHIFT
.globl __entry_tramp_data_start
__entry_tramp_data_start:
- .quad vectors
- .popsection // .rodata
+ .irpc i, 01234567
+alternative_cb tramp_patch_vectors_address
+ movz x30, :abs_g3:0
+ movk x30, :abs_g2_nc:0
+ movk x30, :abs_g1_nc:0
+ movk x30, :abs_g0_nc:0
+alternative_cb_end
+ prfm plil1strm, [x30, #(0x400 + \i * 0x80)]
+ msr vbar_el1, x30
+ add x30, x30, 0x400 + \i * 0x80
+ isb
+ br x30
+ .endr
+ .set .Ltramp_stage2_size, (. - __entry_tramp_data_start) / 8
+ .popsection // .text
#endif /* CONFIG_RANDOMIZE_BASE */
#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 916d9ced1c3f..4a9788e76489 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -547,13 +547,38 @@ static int __init map_entry_trampoline(void)
extern char __entry_tramp_data_start[];
__set_fixmap(FIX_ENTRY_TRAMP_DATA,
- __pa_symbol(__entry_tramp_data_start),
- PAGE_KERNEL_RO);
+ __pa_symbol(__entry_tramp_data_start), prot);
}
return 0;
}
core_initcall(map_entry_trampoline);
+
+#ifdef CONFIG_RANDOMIZE_BASE
+void __init tramp_patch_vectors_address(struct alt_instr *alt,
+ __le32 *origptr, __le32 *updptr,
+ int nr_inst)
+{
+ enum aarch64_insn_movewide_type type;
+ int s;
+
+ /* We only expect a 4 instruction sequence */
+ BUG_ON(nr_inst != 4);
+
+ type = AARCH64_INSN_MOVEWIDE_ZERO;
+ for (s = 0; nr_inst--; s += 16) {
+ extern const char vectors[];
+
+ u32 insn = aarch64_insn_gen_movewide(AARCH64_INSN_REG_30,
+ (u16)((u64)vectors >> s),
+ s,
+ AARCH64_INSN_VARIANT_64BIT,
+ type);
+ *updptr++ = cpu_to_le32(insn);
+ type = AARCH64_INSN_MOVEWIDE_KEEP;
+ }
+}
+#endif
#endif
/*
next prev parent reply other threads:[~2018-01-06 13:13 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-05 13:12 [PATCH v2 00/11] arm64 kpti hardening and variant 2 workarounds Will Deacon
2018-01-05 13:12 ` [PATCH v2 01/11] arm64: use RET instruction for exiting the trampoline Will Deacon
2018-01-06 13:13 ` Ard Biesheuvel [this message]
2018-01-08 14:33 ` Will Deacon
2018-01-08 14:38 ` Ard Biesheuvel
2018-01-08 14:45 ` Will Deacon
2018-01-08 14:56 ` Ard Biesheuvel
2018-01-08 15:27 ` David Laight
2018-01-05 13:12 ` [PATCH v2 02/11] arm64: Kconfig: Reword UNMAP_KERNEL_AT_EL0 kconfig entry Will Deacon
2018-01-05 13:12 ` [PATCH v2 03/11] arm64: Take into account ID_AA64PFR0_EL1.CSV3 Will Deacon
2018-01-08 7:24 ` [v2,03/11] " Jayachandran C
2018-01-08 9:20 ` Marc Zyngier
2018-01-08 17:40 ` Jayachandran C
2018-01-08 17:51 ` Will Deacon
2018-01-08 18:22 ` Alan Cox
2018-01-09 4:06 ` Jayachandran C
2018-01-09 10:00 ` Will Deacon
2018-01-19 1:00 ` Jon Masters
2018-01-08 17:52 ` Marc Zyngier
2018-01-08 17:06 ` Will Deacon
2018-01-08 17:50 ` Jayachandran C
2018-01-05 13:12 ` [PATCH v2 04/11] arm64: cpufeature: Pass capability structure to ->enable callback Will Deacon
2018-01-05 13:12 ` [PATCH v2 05/11] drivers/firmware: Expose psci_get_version through psci_ops structure Will Deacon
2018-01-05 13:12 ` [PATCH v2 06/11] arm64: Move post_ttbr_update_workaround to C code Will Deacon
2018-01-05 13:12 ` [PATCH v2 07/11] arm64: Add skeleton to harden the branch predictor against aliasing attacks Will Deacon
2018-01-08 0:15 ` Jon Masters
2018-01-08 12:16 ` James Morse
2018-01-08 14:26 ` Will Deacon
2018-01-17 4:10 ` Yisheng Xie
2018-01-17 10:07 ` Will Deacon
2018-01-18 8:37 ` Yisheng Xie
2018-01-19 3:37 ` Li Kun
2018-01-19 14:28 ` Will Deacon
2018-01-22 6:52 ` Li Kun
2018-01-05 13:12 ` [PATCH v2 08/11] arm64: KVM: Use per-CPU vector when BP hardening is enabled Will Deacon
2018-01-05 13:12 ` [PATCH v2 09/11] arm64: KVM: Make PSCI_VERSION a fast path Will Deacon
2018-01-05 13:12 ` [PATCH v2 10/11] arm64: cputype: Add missing MIDR values for Cortex-A72 and Cortex-A75 Will Deacon
2018-01-05 13:12 ` [PATCH v2 11/11] arm64: Implement branch predictor hardening for affected Cortex-A CPUs Will Deacon
2018-01-05 14:46 ` James Morse
2018-01-05 14:57 ` Marc Zyngier
2018-01-08 6:31 ` [v2, " Jayachandran C
2018-01-08 6:53 ` [PATCH 1/2] arm64: cputype: Add MIDR values for Cavium ThunderX2 CPUs Jayachandran C
2018-01-08 6:53 ` [PATCH 2/2] arm64: Branch predictor hardening for Cavium ThunderX2 Jayachandran C
2018-01-08 16:46 ` Will Deacon
2018-01-08 17:19 ` Jayachandran C
2018-01-08 17:23 ` Will Deacon
2018-01-09 2:26 ` Jayachandran C
2018-01-09 9:53 ` Will Deacon
2018-01-09 12:47 ` [PATCH v2] " Jayachandran C
2018-01-16 21:50 ` Jon Masters
2018-01-16 21:52 ` Jon Masters
2018-01-16 23:45 ` Jayachandran C
2018-01-17 18:34 ` Jon Masters
2018-01-18 13:53 ` Will Deacon
2018-01-18 17:56 ` Jayachandran C
2018-01-18 18:27 ` Jon Masters
2018-01-18 23:28 ` Jayachandran C
2018-01-19 1:17 ` Jon Masters
2018-01-19 12:22 ` [PATCH v3 1/2] " Jayachandran C
2018-01-19 12:22 ` [PATCH v3 2/2] arm64: Turn on KPTI only on CPUs that need it Jayachandran C
2018-01-22 11:41 ` Will Deacon
2018-01-22 11:51 ` Ard Biesheuvel
2018-01-22 11:55 ` Will Deacon
2018-01-22 18:59 ` Jon Masters
2018-01-19 19:08 ` [PATCH v3 1/2] arm64: Branch predictor hardening for Cavium ThunderX2 Jon Masters
2018-01-22 11:33 ` Will Deacon
2018-01-22 19:00 ` Jon Masters
2018-01-23 9:51 ` Will Deacon
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