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Message-ID: <20140819123342.GJ23128@arm.com>
Date: Tue, 19 Aug 2014 13:33:42 +0100
From: Will Deacon <will.deacon@....com>
To: Kees Cook <keescook@...omium.org>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Rob Herring <robh@...nel.org>,
Laura Abbott <lauraa@...eaurora.org>,
Leif Lindholm <leif.lindholm@...aro.org>,
Stephen Boyd <sboyd@...eaurora.org>,
"msalter@...hat.com" <msalter@...hat.com>,
Rabin Vincent <rabin@....in>, Liu hua <sdu.liu@...wei.com>,
Nikolay Borisov <Nikolay.Borisov@....com>,
Nicolas Pitre <nicolas.pitre@...aro.org>,
Tomasz Figa <t.figa@...sung.com>,
Doug Anderson <dianders@...gle.com>,
Jason Wessel <jason.wessel@...driver.com>,
Catalin Marinas <Catalin.Marinas@....com>,
Russell King - ARM Linux <linux@....linux.org.uk>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v4 7/8] ARM: mm: allow non-text sections to be
non-executable
On Wed, Aug 13, 2014 at 06:06:32PM +0100, Kees Cook wrote:
> Adds CONFIG_ARM_KERNMEM_PERMS to separate the kernel memory regions
> into section-sized areas that can have different permisions. Performs
> the NX permission changes during free_initmem, so that init memory can be
> reclaimed.
>
> This uses section size instead of PMD size to reduce memory lost to
> padding on non-LPAE systems.
>
> Based on work by Brad Spengler, Larry Bassel, and Laura Abbott.
[...]
> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> index 6f57cb94367f..a3d07ca2bbb4 100644
> --- a/arch/arm/kernel/vmlinux.lds.S
> +++ b/arch/arm/kernel/vmlinux.lds.S
> @@ -8,6 +8,9 @@
> #include <asm/thread_info.h>
> #include <asm/memory.h>
> #include <asm/page.h>
> +#ifdef CONFIG_ARM_KERNMEM_PERMS
> +#include <asm/pgtable.h>
> +#endif
>
> #define PROC_INFO \
> . = ALIGN(4); \
> @@ -90,6 +93,11 @@ SECTIONS
> _text = .;
> HEAD_TEXT
> }
> +
> +#ifdef CONFIG_ARM_KERNMEM_PERMS
> + . = ALIGN(1<<SECTION_SHIFT);
> +#endif
> +
> .text : { /* Real text segment */
> _stext = .; /* Text and read-only data */
> __exception_text_start = .;
> @@ -145,7 +153,11 @@ SECTIONS
> _etext = .; /* End of text and rodata section */
>
> #ifndef CONFIG_XIP_KERNEL
> +# ifdef CONFIG_ARM_KERNMEM_PERMS
> + . = ALIGN(1<<SECTION_SHIFT);
> +# else
> . = ALIGN(PAGE_SIZE);
> +# endif
This might be cleaner if we had a single macro (ALIGN_MIN?) that expanded to
ALIGN(1 << SECTION_SHIFT) #ifdef CONFIG_ARM_KERNMEM_PERMS.
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index ad82c05bfc3a..ccf392ef40d4 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -32,6 +32,11 @@
> #include <asm/tlb.h>
> #include <asm/fixmap.h>
>
> +#ifdef CONFIG_ARM_KERNMEM_PERMS
> +#include <asm/system_info.h>
> +#include <asm/cp15.h>
> +#endif
We already #include cp15.h in this file. If you need system_info.h, I don't
think you should bother making the include conditional.
> +/*
> + * Updates section permissions only for the current mm (sections are
> + * copied into each mm). During startup, this is the init_mm.
> + */
> +static inline void section_update(unsigned long addr, pmdval_t mask,
> + pmdval_t prot)
> +{
> + struct mm_struct *mm;
> + pmd_t *pmd;
> +
> + mm = current->active_mm;
> + pmd = pmd_offset(pud_offset(pgd_offset(mm, addr), addr), addr);
> +
> +#ifdef CONFIG_ARM_LPAE
> + pmd[0] = __pmd((pmd_val(pmd[0]) & mask) | prot);
> +#else
> + if (addr & SECTION_SIZE)
> + pmd[1] = __pmd((pmd_val(pmd[1]) & mask) | prot);
> + else
> + pmd[0] = __pmd((pmd_val(pmd[0]) & mask) | prot);
> +#endif
> + flush_pmd_entry(pmd);
> + local_flush_tlb_kernel_range(addr, addr + SECTION_SIZE);
Why only a local flush? You're changing global mappings here, right?
> +}
> +
> +/* Make sure extended page tables are in use. */
> +static inline bool arch_has_strict_perms(void)
> +{
> + unsigned int cr;
> +
> + if (cpu_architecture() < CPU_ARCH_ARMv6)
> + return false;
> +
> + cr = get_cr();
> + if (!(cr & CR_XP))
> + return false;
> +
> + return true;
return !!(get_cr() & CR_XP)?
> +}
> +
> +#define set_section_perms(perms, field) { \
> + size_t i; \
> + unsigned long addr; \
> + \
> + if (!arch_has_strict_perms()) \
> + return; \
> + \
> + for (i = 0; i < ARRAY_SIZE(perms); i++) { \
> + if (!IS_ALIGNED(perms[i].start, SECTION_SIZE) || \
> + !IS_ALIGNED(perms[i].end, SECTION_SIZE)) { \
> + pr_err("BUG: section %lx-%lx not aligned to %lx\n", \
> + perms[i].start, perms[i].end, \
> + SECTION_SIZE); \
> + continue; \
> + } \
> + \
> + for (addr = perms[i].start; \
> + addr < perms[i].end; \
> + addr += SECTION_SIZE) \
> + section_update(addr, perms[i].mask, \
> + perms[i].field); \
> + } \
> +}
> +
> +static inline void fix_kernmem_perms(void)
> +{
> + set_section_perms(nx_perms, prot);
> +}
> +#else
> +static inline void fix_kernmem_perms(void) { }
> +#endif /* CONFIG_ARM_KERNMEM_PERMS */
> +
> void free_initmem(void)
> {
> #ifdef CONFIG_HAVE_TCM
> extern char __tcm_start, __tcm_end;
> +#endif
> +
> + fix_kernmem_perms();
>
> +#ifdef CONFIG_HAVE_TCM
You could avoid the double #ifdef by moving the tcm stuff into another
function (free_tcmmem?)
Will
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