Re: [PATCH -next v5 2/8] arm64: extable: make uaaccess helper use extable type EX_TYPE_UACCESS_ERR_ZERO

From: Tong Tiangen
Date: Sat Jun 18 2022 - 04:42:14 EST




在 2022/6/18 11:26, Tong Tiangen 写道:


在 2022/6/17 16:24, Mark Rutland 写道:
On Sat, May 28, 2022 at 06:50:50AM +0000, Tong Tiangen wrote:
Currnetly, the extable type used by __arch_copy_from/to_user() is
EX_TYPE_FIXUP. In fact, It is more clearly to use meaningful
EX_TYPE_UACCESS_*.

Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Tong Tiangen <tongtiangen@xxxxxxxxxx>
---
  arch/arm64/include/asm/asm-extable.h |  8 ++++++++
  arch/arm64/include/asm/asm-uaccess.h | 12 ++++++------
  2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/asm-extable.h b/arch/arm64/include/asm/asm-extable.h
index 56ebe183e78b..9c94ac1f082c 100644
--- a/arch/arm64/include/asm/asm-extable.h
+++ b/arch/arm64/include/asm/asm-extable.h
@@ -28,6 +28,14 @@
      __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_FIXUP, 0)
      .endm
+/*
+ * Create an exception table entry for uaccess `insn`, which will branch to `fixup`
+ * when an unhandled fault is taken.
+ * ex->data = ~0 means both reg_err and reg_zero is set to wzr(x31).
+ */
+    .macro          _asm_extable_uaccess, insn, fixup
+    __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_UACCESS_ERR_ZERO, ~0)
+    .endm

I'm not too keen on using `~0` here, since that also sets other bits in the
data field, and its somewhat opaque.

How painful is it to generate the data fields as with the C version of this
macro, so that we can pass in wzr explciitly for the two sub-fields?

Other than that, this looks good to me.

Thanks,
Mark.

ok, will fix next version.

Thanks,
Tong.

I tried to using data filelds as with C version, but here assembly code we can not using operator such as << and |, if we use lsl and orr instructions, the gpr will be occupied.

So how about using 0x3ff directly here? it means err register and zero register both set to x31.

Thanks,
Tong.



  /*
   * Create an exception table entry for `insn` if `fixup` is provided. Otherwise
   * do nothing.
diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
index 0557af834e03..75b211c98dea 100644
--- a/arch/arm64/include/asm/asm-uaccess.h
+++ b/arch/arm64/include/asm/asm-uaccess.h
@@ -61,7 +61,7 @@ alternative_else_nop_endif
  #define USER(l, x...)                \
  9999:    x;                    \
-    _asm_extable    9999b, l
+    _asm_extable_uaccess    9999b, l
  /*
   * Generate the assembly for LDTR/STTR with exception table entries.
@@ -73,8 +73,8 @@ alternative_else_nop_endif
  8889:        ldtr    \reg2, [\addr, #8];
          add    \addr, \addr, \post_inc;
-        _asm_extable    8888b,\l;
-        _asm_extable    8889b,\l;
+        _asm_extable_uaccess    8888b, \l;
+        _asm_extable_uaccess    8889b, \l;
      .endm
      .macro user_stp l, reg1, reg2, addr, post_inc
@@ -82,14 +82,14 @@ alternative_else_nop_endif
  8889:        sttr    \reg2, [\addr, #8];
          add    \addr, \addr, \post_inc;
-        _asm_extable    8888b,\l;
-        _asm_extable    8889b,\l;
+        _asm_extable_uaccess    8888b,\l;
+        _asm_extable_uaccess    8889b,\l;
      .endm
      .macro user_ldst l, inst, reg, addr, post_inc
  8888:        \inst        \reg, [\addr];
          add        \addr, \addr, \post_inc;
-        _asm_extable    8888b,\l;
+        _asm_extable_uaccess    8888b, \l;
      .endm
  #endif
--
2.25.1

.

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