Re: [PATCH v2] riscv: Map the kernel with correct permissions the first time
From: Palmer Dabbelt
Date: Sat May 29 2021 - 16:38:14 EST
On Fri, 28 May 2021 01:24:43 PDT (-0700), alex@xxxxxxxx wrote:
Hi Christoph,
Le 27/05/2021 à 08:35, Christoph Hellwig a écrit :
On Wed, May 26, 2021 at 03:41:10PM +0200, Alexandre Ghiti wrote:
#ifdef CONFIG_64BIT
+#define is_kernel_mapping(x) ((x) >= kernel_virt_addr && (x) < (kernel_virt_addr + load_sz))
+#define is_linear_mapping(x) ((x) >= PAGE_OFFSET && (x) < kernel_virt_addr)
+
Overly long lines. Independ of that complex macros are generally much
more readable if they are written more function-like, that is the name
and paramtes are kept on a line of their own:
#define is_kernel_mapping(x) \
((x) >= kernel_virt_addr && (x) < (kernel_virt_addr + load_sz))
But what is the reason to not make them type-safe inline functions
anyway?
No reason. I will then make those macros inline functions and send
another patchset to make the below macro an inline function too.
#define __va_to_pa_nodebug(x) ({ \
unsigned long _x = x; \
- (_x < kernel_virt_addr) ? \
+ is_linear_mapping(_x) ? \
linear_mapping_va_to_pa(_x) : kernel_mapping_va_to_pa(_x); \
})
... especially for something complex like this.
+static inline bool is_va_kernel_lm_alias_text(uintptr_t va)
+{
+ return (va >= (uintptr_t)lm_alias(_start) && va < (uintptr_t)lm_alias(__init_text_begin));
Overly long line as well. And useless braces.
Ok.
+static inline bool is_va_kernel_init_text(uintptr_t va)
+{
+ return (va >= (uintptr_t)__init_text_begin && va < (uintptr_t)__init_data_begin);
+}
Same here.
checkpatch does not complain about those lines which are under 100
characters, what's the point in breaking them on multiple lines?
+#ifdef CONFIG_STRICT_KERNEL_RWX
+static __init pgprot_t pgprot_from_va(uintptr_t va)
+{
+#ifdef CONFIG_64BIT
+ if (is_va_kernel_text(va) || is_va_kernel_init_text(va))
+ return PAGE_KERNEL_READ_EXEC;
+
+ /*
+ * We must mark only text as read-only as init text will get freed later
+ * and rodata section is marked readonly in mark_rodata_ro.
+ */
+ if (is_va_kernel_lm_alias_text(va))
+ return PAGE_KERNEL_READ;
+
+ return PAGE_KERNEL;
+#else
+ if (is_va_kernel_text(va))
+ return PAGE_KERNEL_READ_EXEC;
+
+ if (is_va_kernel_init_text(va))
+ return PAGE_KERNEL_EXEC;
+
+ return PAGE_KERNEL;
+#endif /* CONFIG_64BIT */
+}
If the entire function is different for config symbols please just
split it into two separate functions. But to make the difference more
clear IS_ENABLED might fit better here:
static __init pgprot_t pgprot_from_va(uintptr_t va)
{
if (is_va_kernel_text(va))
return PAGE_KERNEL_READ_EXEC;
if (is_va_kernel_init_text(va))
return IS_ENABLED(CONFIG_64BIT) ?
PAGE_KERNEL_READ_EXEC : PAGE_KERNEL_EXEC;
if (IS_ENABLED(CONFIG_64BIT) && is_va_kernel_lm_alias_text(va))
return PAGE_KERNEL_READ;
return PAGE_KERNEL;
}
Preferable with comments explaining the 32-bit vs 64-bit difference.
Ok this is more compact, I'll do that with the comment.
+void mark_rodata_ro(void)
+{
+ unsigned long rodata_start = (unsigned long)__start_rodata;
+ unsigned long data_start = (unsigned long)_data;
+ unsigned long __maybe_unused lm_rodata_start = (unsigned long)lm_alias(__start_rodata);
+ unsigned long __maybe_unused lm_data_start = (unsigned long)lm_alias(_data);
+
+ set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
+#ifdef CONFIG_64BIT
+ set_memory_ro(lm_rodata_start, (lm_data_start - lm_rodata_start) >> PAGE_SHIFT);
+#endif
Lots of unreadable overly lone lines. Why not add a helper and do
something like:
static void set_kernel_memory_ro(char *startp, char *endp)
{
unsigned long start = (unsigned long)startp;
unsigned long end = (unsigned long)endp;
set_memory_ro(start, (start - end) >> PAGE_SHIFT);
}
set_kernel_memory_ro(_start_rodata, _data);
if (IS_ENABLED(CONFIG_64BIT))
set_kernel_memory_ro(lm_alias(__start_rodata), lm_alias(_data));
Ok, that's better indeed. I will do something like that instead, to
avoid multiple versions of this helper:
int set_kernel_memory(char *startp, char *endp,
int (*set_memory)(unsigned long start, int
num_pages))
+static __init pgprot_t pgprot_from_va(uintptr_t va)
+{
+#ifdef CONFIG_64BIT
+ if (is_kernel_mapping(va))
+ return PAGE_KERNEL_EXEC;
+
+ if (is_linear_mapping(va))
+ return PAGE_KERNEL;
+
+ return PAGE_KERNEL;
+#else
+ return PAGE_KERNEL_EXEC;
+#endif /* CONFIG_64BIT */
+}
+#endif /* CONFIG_STRICT_KERNEL_RWX */
+
Same comment as for the other version. This could become:
static __init pgprot_t pgprot_from_va(uintptr_t va)
{
if (IS_ENABLED(CONFIG_64BIT) && !is_kernel_mapping(va))
return PAGE_KERNEL;
return PAGE_KERNEL_EXEC;
}
Ok I'll do that.
-static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
+static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size, bool early)
Overly long line.
for (va = kernel_virt_addr; va < end_va; va += map_size)
create_pgd_mapping(pgdir, va,
load_pa + (va - kernel_virt_addr),
- map_size, PAGE_KERNEL_EXEC);
+ map_size, early ? PAGE_KERNEL_EXEC : pgprot_from_va(va));
Same here. But why not pass in a "pgprot_t ram_pgprot" instead of the
bool, which would be self-documenting.
This function is used to map the kernel mapping, the pgprot_t is then
different in create_kernel_page_table depending on the virtual address
so I can't pass a single pgprot_t for that or I would need a dummy
pgprot_t to test anyway.
Thanks. I've got a riscv-wx-mappings branch with the fix on it, I'll
take this on there when we have something ready to go and then merge
both into for-next so we can avoid merge conflicts.
Thank you for your review,
Alex
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