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riscv: extend patch_text_nosync() for multiple pages
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The patch_insn_write() function currently doesn't work for multiple pages
of instructions, therefore patch_text_nosync() will fail with a page fault
if called with lengths spanning multiple pages.

This commit extends the patch_insn_write() function to support multiple
pages by copying at max 2 pages at a time in a loop. This implementation
is similar to text_poke_copy() function of x86.

Signed-off-by: Puranjay Mohan <[email protected]>
Reviewed-by: Pu Lehui <[email protected]>
Reviewed-by: Björn Töpel <[email protected]>
Tested-by: Björn Töpel <[email protected]>
Acked-by: Daniel Borkmann <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>
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puranjaymohan authored and palmer-dabbelt committed Sep 6, 2023
1 parent 20e490a commit 9721873
Showing 1 changed file with 32 additions and 5 deletions.
37 changes: 32 additions & 5 deletions arch/riscv/kernel/patch.c
Original file line number Diff line number Diff line change
Expand Up @@ -53,12 +53,18 @@ static void patch_unmap(int fixmap)
}
NOKPROBE_SYMBOL(patch_unmap);

static int patch_insn_write(void *addr, const void *insn, size_t len)
static int __patch_insn_write(void *addr, const void *insn, size_t len)
{
void *waddr = addr;
bool across_pages = (((uintptr_t) addr & ~PAGE_MASK) + len) > PAGE_SIZE;
int ret;

/*
* Only two pages can be mapped at a time for writing.
*/
if (len + offset_in_page(addr) > 2 * PAGE_SIZE)
return -EINVAL;

/*
* Before reaching here, it was expected to lock the text_mutex
* already, so we don't need to give another lock here and could
Expand All @@ -74,7 +80,7 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
lockdep_assert_held(&text_mutex);

if (across_pages)
patch_map(addr + len, FIX_TEXT_POKE1);
patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);

waddr = patch_map(addr, FIX_TEXT_POKE0);

Expand All @@ -87,15 +93,36 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)

return ret;
}
NOKPROBE_SYMBOL(patch_insn_write);
NOKPROBE_SYMBOL(__patch_insn_write);
#else
static int patch_insn_write(void *addr, const void *insn, size_t len)
static int __patch_insn_write(void *addr, const void *insn, size_t len)
{
return copy_to_kernel_nofault(addr, insn, len);
}
NOKPROBE_SYMBOL(patch_insn_write);
NOKPROBE_SYMBOL(__patch_insn_write);
#endif /* CONFIG_MMU */

static int patch_insn_write(void *addr, const void *insn, size_t len)
{
size_t patched = 0;
size_t size;
int ret = 0;

/*
* Copy the instructions to the destination address, two pages at a time
* because __patch_insn_write() can only handle len <= 2 * PAGE_SIZE.
*/
while (patched < len && !ret) {
size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
ret = __patch_insn_write(addr + patched, insn + patched, size);

patched += size;
}

return ret;
}
NOKPROBE_SYMBOL(patch_insn_write);

int patch_text_nosync(void *addr, const void *insns, size_t len)
{
u32 *tp = addr;
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