Re: [PATCH v9 3/8] powerpc/kprobes: Mark newly allocated probes as RO
From: Christophe Leroy <hidden>
Date: 2021-03-16 06:45:19
Le 16/03/2021 à 04:17, Jordan Niethe a écrit :
From: Russell Currey <redacted> With CONFIG_STRICT_KERNEL_RWX=y and CONFIG_KPROBES=y, there will be one W+X page at boot by default. This can be tested with CONFIG_PPC_PTDUMP=y and CONFIG_PPC_DEBUG_WX=y set, and checking the kernel log during boot.
This text is confusing. I don't understand what is the status before the patch, and what is the status after. "there will be one ...", does it mean after the patch ?
Add an arch specific insn page allocator which returns RO pages if STRICT_KERNEL_RWX is enabled. This page is only written to with patch_instruction() which is able to write RO pages.
"an" or "the" arch specific insn page allocator ?
quoted hunk ↗ jump to hunk
Reviewed-by: Daniel Axtens <redacted> Signed-off-by: Russell Currey <redacted> Signed-off-by: Christophe Leroy <redacted> [jpn: Reword commit message, switch from vmalloc_exec(), add free_insn_page()] Signed-off-by: Jordan Niethe <redacted> --- v9: - vmalloc_exec() no longer exists - Set the page to RW before freeing it --- arch/powerpc/kernel/kprobes.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c index 01ab2163659e..bb7e4d321988 100644 --- a/arch/powerpc/kernel/kprobes.c +++ b/arch/powerpc/kernel/kprobes.c@@ -25,6 +25,8 @@ #include <asm/sections.h> #include <asm/inst.h> #include <linux/uaccess.h> +#include <linux/set_memory.h> +#include <linux/vmalloc.h> DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL; DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);@@ -103,6 +105,26 @@ kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset) return addr; } +void *alloc_insn_page(void) +{ + void *page = vmalloc(PAGE_SIZE);
Can't do that on book3s/32, see https://github.com/linuxppc/linux/commit/6ca05532 and https://github.com/linuxppc/linux/commit/7fbc22ce Should do: return __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END, GFP_KERNEL, PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS, NUMA_NO_NODE, __builtin_return_address(0)); To keep it simple, you'll probably need to define MODULES_VADDR and MODULES_END as resp VMALLOC_START and VMALLOC_END when they are not defined, maybe in asm/pgtable.h
+
+ if (!page)
+ return NULL;
+
+ set_memory_ro((unsigned long)page, 1);
+ set_memory_x((unsigned long)page, 1);
+
+ return page;
+}
+
+void free_insn_page(void *page)
+{
+ set_memory_nx((unsigned long)page, 1);
+ set_memory_rw((unsigned long)page, 1);
+ vfree(page);
+}
+
int arch_prepare_kprobe(struct kprobe *p)
{
int ret = 0;