From e27d90e8be08d96b5e047cd01daf7e62c4fcab78 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Tue, 22 Dec 2015 10:39:54 +1030 Subject: [PATCH] lguest: Map switcher text R/O Pavel noted that lguest maps the switcher code executable and read-write. This is a bad idea for any kernel text, but particularly for text mapped at a fixed address. Create two vmas, one for the text (PAGE_KERNEL_RX) and another for the stacks (PAGE_KERNEL). Use VM_NO_GUARD to map them adjacent (as expected by the rest of the code). Reported-by: Pavel Machek Tested-by: Pavel Machek Signed-off-by: Rusty Russell Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- arch/x86/include/asm/lguest.h | 4 +- drivers/lguest/core.c | 74 ++++++++++++++++++++++++----------- 2 files changed, 54 insertions(+), 24 deletions(-) diff --git a/arch/x86/include/asm/lguest.h b/arch/x86/include/asm/lguest.h index 3bbc07a57a31..73d0c9b92087 100644 --- a/arch/x86/include/asm/lguest.h +++ b/arch/x86/include/asm/lguest.h @@ -12,7 +12,9 @@ #define GUEST_PL 1 /* Page for Switcher text itself, then two pages per cpu */ -#define TOTAL_SWITCHER_PAGES (1 + 2 * nr_cpu_ids) +#define SWITCHER_TEXT_PAGES (1) +#define SWITCHER_STACK_PAGES (2 * nr_cpu_ids) +#define TOTAL_SWITCHER_PAGES (SWITCHER_TEXT_PAGES + SWITCHER_STACK_PAGES) /* Where we map the Switcher, in both Host and Guest. */ extern unsigned long switcher_addr; diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c index 312ffd3d0017..9e385b38debf 100644 --- a/drivers/lguest/core.c +++ b/drivers/lguest/core.c @@ -22,7 +22,8 @@ unsigned long switcher_addr; struct page **lg_switcher_pages; -static struct vm_struct *switcher_vma; +static struct vm_struct *switcher_text_vma; +static struct vm_struct *switcher_stacks_vma; /* This One Big lock protects all inter-guest data structures. */ DEFINE_MUTEX(lguest_lock); @@ -82,55 +83,81 @@ static __init int map_switcher(void) } } + /* + * Copy in the compiled-in Switcher code (from x86/switcher_32.S). + * It goes in the first page, which we map in momentarily. + */ + memcpy(kmap(lg_switcher_pages[0]), start_switcher_text, + end_switcher_text - start_switcher_text); + kunmap(lg_switcher_pages[0]); + /* * We place the Switcher underneath the fixmap area, which is the * highest virtual address we can get. This is important, since we * tell the Guest it can't access this memory, so we want its ceiling * as high as possible. */ - switcher_addr = FIXADDR_START - (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE; + switcher_addr = FIXADDR_START - TOTAL_SWITCHER_PAGES*PAGE_SIZE; /* - * Now we reserve the "virtual memory area" we want. We might - * not get it in theory, but in practice it's worked so far. - * The end address needs +1 because __get_vm_area allocates an - * extra guard page, so we need space for that. + * Now we reserve the "virtual memory area"s we want. We might + * not get them in theory, but in practice it's worked so far. + * + * We want the switcher text to be read-only and executable, and + * the stacks to be read-write and non-executable. */ - switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE, - VM_ALLOC, switcher_addr, switcher_addr - + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE); - if (!switcher_vma) { + switcher_text_vma = __get_vm_area(PAGE_SIZE, VM_ALLOC|VM_NO_GUARD, + switcher_addr, + switcher_addr + PAGE_SIZE); + + if (!switcher_text_vma) { err = -ENOMEM; printk("lguest: could not map switcher pages high\n"); goto free_pages; } + switcher_stacks_vma = __get_vm_area(SWITCHER_STACK_PAGES * PAGE_SIZE, + VM_ALLOC|VM_NO_GUARD, + switcher_addr + PAGE_SIZE, + switcher_addr + TOTAL_SWITCHER_PAGES * PAGE_SIZE); + if (!switcher_stacks_vma) { + err = -ENOMEM; + printk("lguest: could not map switcher pages high\n"); + goto free_text_vma; + } + /* * This code actually sets up the pages we've allocated to appear at * switcher_addr. map_vm_area() takes the vma we allocated above, the - * kind of pages we're mapping (kernel pages), and a pointer to our - * array of struct pages. + * kind of pages we're mapping (kernel text pages and kernel writable + * pages respectively), and a pointer to our array of struct pages. */ - err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, lg_switcher_pages); + err = map_vm_area(switcher_text_vma, PAGE_KERNEL_RX, lg_switcher_pages); + if (err) { + printk("lguest: text map_vm_area failed: %i\n", err); + goto free_vmas; + } + + err = map_vm_area(switcher_stacks_vma, PAGE_KERNEL, + lg_switcher_pages + SWITCHER_TEXT_PAGES); if (err) { - printk("lguest: map_vm_area failed: %i\n", err); - goto free_vma; + printk("lguest: stacks map_vm_area failed: %i\n", err); + goto free_vmas; } /* * Now the Switcher is mapped at the right address, we can't fail! - * Copy in the compiled-in Switcher code (from x86/switcher_32.S). */ - memcpy(switcher_vma->addr, start_switcher_text, - end_switcher_text - start_switcher_text); - printk(KERN_INFO "lguest: mapped switcher at %p\n", - switcher_vma->addr); + switcher_text_vma->addr); /* And we succeeded... */ return 0; -free_vma: - vunmap(switcher_vma->addr); +free_vmas: + /* Undoes map_vm_area and __get_vm_area */ + vunmap(switcher_stacks_vma->addr); +free_text_vma: + vunmap(switcher_text_vma->addr); free_pages: i = TOTAL_SWITCHER_PAGES; free_some_pages: @@ -148,7 +175,8 @@ static void unmap_switcher(void) unsigned int i; /* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */ - vunmap(switcher_vma->addr); + vunmap(switcher_text_vma->addr); + vunmap(switcher_stacks_vma->addr); /* Now we just need to free the pages we copied the switcher into */ for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) __free_pages(lg_switcher_pages[i], 0); -- 2.20.1