From mboxrd@z Thu Jan 1 00:00:00 1970 From: ard.biesheuvel@linaro.org (Ard Biesheuvel) Date: Wed, 18 Mar 2015 15:55:27 +0100 Subject: [PATCH v5 8/8] arm64: enforce x1|x2|x3 == 0 upon kernel entry as per boot protocol In-Reply-To: <1426690527-14258-1-git-send-email-ard.biesheuvel@linaro.org> References: <1426690527-14258-1-git-send-email-ard.biesheuvel@linaro.org> Message-ID: <1426690527-14258-9-git-send-email-ard.biesheuvel@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org According to the arm64 boot protocol, registers x1 to x3 should be zero upon kernel entry, and non-zero values are reserved for future use. This future use is going to be problematic if we never enforce the current rules, so start enforcing them now, by emitting a warning if non-zero values are detected. Signed-off-by: Ard Biesheuvel --- arch/arm64/kernel/head.S | 4 ++++ arch/arm64/kernel/setup.c | 15 +++++++++++++++ 2 files changed, 19 insertions(+) diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index a0fbd99efb89..8636c3cef006 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -233,6 +233,10 @@ section_table: #endif ENTRY(stext) + adr_l x8, boot_regs // record the contents of + stp x0, x1, [x8] // x0 .. x3 at kernel entry + stp x2, x3, [x8, #16] + mov x21, x0 // x21=FDT bl el2_setup // Drop to EL1, w20=cpu_boot_mode adrp x24, __PHYS_OFFSET diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c index 6c5fb5aff325..2d5cae2de679 100644 --- a/arch/arm64/kernel/setup.c +++ b/arch/arm64/kernel/setup.c @@ -114,6 +114,11 @@ void __init early_print(const char *str, ...) printk("%s", buf); } +/* + * The recorded values of x0 .. x3 upon kernel entry. + */ +u64 __read_mostly boot_regs[4]; + void __init smp_setup_processor_id(void) { u64 mpidr = read_cpuid_mpidr() & MPIDR_HWID_BITMASK; @@ -387,6 +392,16 @@ void __init setup_arch(char **cmdline_p) conswitchp = &dummy_con; #endif #endif + /* + * boot_regs[] is written by the boot CPU with the caches off, so we + * need to ensure that we read the value from main memory + */ + __flush_dcache_area(boot_regs, sizeof(boot_regs)); + if (boot_regs[1] || boot_regs[2] || boot_regs[3]) { + pr_err("WARNING: boot protocol violation detected (x1 == %llx, x2 == %llx, x3 == %llx)\n", + boot_regs[1], boot_regs[2], boot_regs[3]); + pr_err("WARNING: your bootloader may fail to load newer kernels\n"); + } } static int __init arm64_device_init(void) -- 1.8.3.2