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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v2 3/4] xen/arm: mpu: Create boot-time MPU protection regions
Hi Ayan, On 18/09/2024 19:51, Ayan Kumar Halder wrote: Define enable_boot_cpu_mm() for the AArch64-V8R system. Like boot-time page table in MMU system, we need a boot-time MPU protection region configuration in MPU system so Xen can fetch code and data from normal memory. To do this, Xen maps the following sections of the binary as separate regions (with permissions) :- 1. Text (Read only at EL2, execution is permitted) 2. RO data (Read only at EL2) 3. RO after init data (Read/Write at EL2 as the data is RW during init) 4. RW data (Read/Write at EL2) 5. BSS (Read/Write at EL2) 6. Init Text (Read only at EL2, execution is permitted) 7. Init data (Read/Write at EL2) If the number of MPU regions created is greater than the count defined in MPUIR_EL2, then the boot fails. One can refer to ARM DDI 0600B.a ID062922 G1.3 "General System Control Registers", to get the definitions of PRBAR_EL2, PRLAR_EL2 and PRSELR_EL2 registers. Also, refer to G1.2 "Accessing MPU memory region registers", the following ``` The MPU provides two register interfaces to program the MPU regions: - Access to any of the MPU regions via PRSELR_ELx, PRBAR<n>_ELx, and PRLAR<n>_ELx. ``` We use the above mechanism to configure the MPU memory regions. MPU specific registers are defined in xen/arch/arm/include/asm/arm64/mpu/sysregs.h. Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx> --- Changes from :- v1 - 1. Instead of mapping a (XEN_START_ADDRESS + 2MB) as a single MPU region, we have separate MPU regions for different parts of the Xen binary. The reason being different regions will nned different permissions (as mentioned in the linker script). 2. Introduced a label (__init_data_begin) to mark the beginning of the init data section. 3. Moved MPU specific register definitions to mpu/sysregs.h. 4. Fixed coding style issues. 5. Included page.h in mpu/head.S as page.h includes sysregs.h. I haven't seen sysregs.h included directly from head.S or mmu/head.S. (Outstanding comment not addressed). xen/arch/arm/Makefile | 1 + xen/arch/arm/arm64/mpu/Makefile | 1 + xen/arch/arm/arm64/mpu/head.S | 176 +++++++++++++++++++ xen/arch/arm/include/asm/arm64/mpu/sysregs.h | 27 +++ xen/arch/arm/include/asm/arm64/sysregs.h | 3 + xen/arch/arm/include/asm/mm.h | 2 + xen/arch/arm/include/asm/mpu/arm64/mm.h | 22 +++ xen/arch/arm/include/asm/mpu/mm.h | 20 +++ xen/arch/arm/xen.lds.S | 1 + 9 files changed, 253 insertions(+) create mode 100644 xen/arch/arm/arm64/mpu/Makefile create mode 100644 xen/arch/arm/arm64/mpu/head.S create mode 100644 xen/arch/arm/include/asm/arm64/mpu/sysregs.h create mode 100644 xen/arch/arm/include/asm/mpu/arm64/mm.h create mode 100644 xen/arch/arm/include/asm/mpu/mm.h diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile index 7792bff597..aebccec63a 100644 --- a/xen/arch/arm/Makefile +++ b/xen/arch/arm/Makefile @@ -1,6 +1,7 @@ obj-$(CONFIG_ARM_32) += arm32/ obj-$(CONFIG_ARM_64) += arm64/ obj-$(CONFIG_MMU) += mmu/ +obj-$(CONFIG_MPU) += mpu/ obj-$(CONFIG_ACPI) += acpi/ obj-$(CONFIG_HAS_PCI) += pci/ ifneq ($(CONFIG_NO_PLAT),y) diff --git a/xen/arch/arm/arm64/mpu/Makefile b/xen/arch/arm/arm64/mpu/Makefile new file mode 100644 index 0000000000..3340058c08 --- /dev/null +++ b/xen/arch/arm/arm64/mpu/Makefile @@ -0,0 +1 @@ +obj-y += head.o diff --git a/xen/arch/arm/arm64/mpu/head.S b/xen/arch/arm/arm64/mpu/head.S new file mode 100644 index 0000000000..ef55c8765c --- /dev/null +++ b/xen/arch/arm/arm64/mpu/head.S @@ -0,0 +1,176 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Start-of-day code for an Armv8-R MPU system. + */ + +#include <asm/mm.h> +#include <asm/page.h> + +#define REGION_TEXT_PRBAR 0x38 /* SH=11 AP=10 XN=00 */ +#define REGION_RO_PRBAR 0x3A /* SH=11 AP=10 XN=10 */ +#define REGION_DATA_PRBAR 0x32 /* SH=11 AP=00 XN=10 */ + +#define REGION_NORMAL_PRLAR 0x0f /* NS=0 ATTR=111 EN=1 */ + +/* + * Macro to round up the section address to be PAGE_SIZE aligned + * Each section(e.g. .text, .data, etc) in xen.lds.S is page-aligned, + * which is usually guarded with ". = ALIGN(PAGE_SIZE)" in the head, + * or in the end + */ +.macro roundup_section, xb + add \xb, \xb, #(PAGE_SIZE-1) + and \xb, \xb, #PAGE_MASK +.endm Can you explain why we need the region to be page-aligned? Would not 64-bytes alignment (IIRC this is the minimum by the MPU sufficient) And more importantly, if those regions were effectively not aligned, would not this mean we would could configure the MPU with two clashing regions? IOW, this round up looks harmful to me. + +/* + * Macro to prepare and set a EL2 MPU memory region. + * We will also create an according MPU memory region entry, which + * is a structure of pr_t, in table \prmap. + * + * Inputs: + * sel: region selector + * base: reg storing base address (should be page-aligned) + * limit: reg storing limit address + * prbar: store computed PRBAR_EL2 value + * prlar: store computed PRLAR_EL2 value + * attr_prbar: PRBAR_EL2-related memory attributes. If not specified it will be + * REGION_DATA_PRBAR + * attr_prlar: PRLAR_EL2-related memory attributes. If not specified it will be + * REGION_NORMAL_PRLAR + * + * Clobber \tmp1, \tmp2 + * + */ +.macro prepare_xen_region, sel, base, limit, prbar, prlar, tmp1, tmp2, attr_prbar=REGION_DATA_PRBAR, attr_prlar=REGION_NORMAL_PRLAR + /* Prepare value for PRBAR_EL2 reg and preserve it in \prbar.*/ + and \base, \base, #MPU_REGION_MASK + mov \prbar, #\attr_prbar + orr \prbar, \prbar, \base + + /* Prepare value for PRLAR_EL2 reg and preserve it in \prlar.*/ + /* Round up limit address to be PAGE_SIZE aligned */ + roundup_section \limit + /* Limit address should be inclusive */ + sub \limit, \limit, #1 + and \limit, \limit, #MPU_REGION_MASK + mov \prlar, #\attr_prlar + orr \prlar, \prlar, \limit + + msr PRSELR_EL2, \sel + isb + msr PRBAR_EL2, \prbar + msr PRLAR_EL2, \prlar + dsb Please use "dsb sy". This has the same meaning as "dsb" but more explicit for the reader. + isb +.endm + +/* Load the physical address of a symbol into xb */ +.macro load_paddr xb, sym + ldr \xb, =\sym + add \xb, \xb, x20 /* x20 - Phys offset */ +.endm + +.section .text.header, "ax", %progbits Does the code below actually need to be in .text.header? + +/* + * Enable EL2 MPU and data cache + * If the Background region is enabled, then the MPU uses the default memory + * map as the Background region for generating the memory + * attributes when MPU is disabled. + * Since the default memory map of the Armv8-R AArch64 architecture is + * IMPLEMENTATION DEFINED, we intend to turn off the Background region here. Based on this sentence, I was expecting an instruction to clear SCTRL_EL2.BR. What did I miss? + * + * Clobbers x0 + * + */ +FUNC_LOCAL(enable_mpu) + mrs x0, SCTLR_EL2 + orr x0, x0, #SCTLR_Axx_ELx_M /* Enable MPU */ + orr x0, x0, #SCTLR_Axx_ELx_C /* Enable D-cache */ + orr x0, x0, #SCTLR_Axx_ELx_WXN /* Enable WXN */ + dsb sy There is no memory access in enable_mpu. So what is this dsb for? + msr SCTLR_EL2, x0 + isb + + ret +END(enable_mpu) + +/* + * Maps the various sections of Xen (described in xen.lds.S) as different MPU + * regions. Some of these regions will be marked read only while the others will + * be read write or execute. And some in the future may need to be memory region (e.g. to use the UART early) :). So how about just dropping it? > + *> + * Inputs: + * lr : Address to return to. + * + * Clobbers x0 - x7 + * + */ +FUNC(enable_boot_cpu_mm) > + mov x7, lr> + + /* x0: region sel */ + mov x0, xzr + /* Xen text section. */ + load_paddr x1, _stext + load_paddr x2, _etext + prepare_xen_region x0, x1, x2, x3, x4, x5, x6, attr_prbar=REGION_TEXT_PRBAR + + add x0, x0, #1 + /* Xen read-only data section. */ + load_paddr x1, _srodata + load_paddr x2, _erodata + prepare_xen_region x0, x1, x2, x3, x4, x5, x6, attr_prbar=REGION_RO_PRBAR + + add x0, x0, #1 + /* Xen read-only after init data section. */ + load_paddr x1, __ro_after_init_start + load_paddr x2, __ro_after_init_end + prepare_xen_region x0, x1, x2, x3, x4, x5, x6 Is it necessary to have a section for the ro-after-init? IOW, could we just fold into... + + add x0, x0, #1 + /* Xen read-write data section. */ + load_paddr x1, __ro_after_init_end + load_paddr x2, __init_begin + prepare_xen_region x0, x1, x2, x3, x4, x5, x6 ... this one during boot and then fold the ro-after-init to the read-only region? This would possibly reduce the number of used by Xen and also avoid reshfulling the MPU section. Another possibility would be to move the ro-after-init MPU region at the end. > +> + add x0, x0, #1 + /* Xen BSS section. */ + load_paddr x1, __bss_start + load_paddr x2, __bss_end + prepare_xen_region x0, x1, x2, x3, x4, x5, x6 + + add x0, x0, #1 + /* Xen init text section. */ + load_paddr x1, __init_begin + load_paddr x2, __init_data_begin + prepare_xen_region x0, x1, x2, x3, x4, x5, x6, attr_prbar=REGION_TEXT_PRBAR + + add x0, x0, #1 + /* Xen init data section. */ + load_paddr x1, __init_data_begin + load_paddr x2, __init_end + prepare_xen_region x0, x1, x2, x3, x4, x5, x6 + + /* Check if the number of regions exceeded the count specified in MPUIR_EL2 */ + mrs x1, MPUIR_EL2 + cmp x0, x1 + bgt 1f + bl enable_mpu It seems to be a bit odd to check *after* we wrote. It would be useful to explain why this is fine.
I would expect the number of user for the MPU sysregs to be limited. So can we include the header only when it is necessary? Cheers, -- Julien Grall
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