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Re: [Xen-devel] [PATCH v5 14/16] livepatch: Initial ARM32 support.



Hi Konrad,

On 21/09/2016 10:32, Konrad Rzeszutek Wilk wrote:
The patch piggybacks on: livepatch: Initial ARM64 support, which
brings up all of the necessary livepatch infrastructure pieces in.

This patch adds three major pieces:

 1) ELF relocations. ARM32 uses SHT_REL instead of SHT_RELA which
    means the adddendum had to be extracted from within the
    instruction. Which required parsing BL/BLX, B/BL<cond>,
    MOVT, and MOVW instructions.

    The code was written from scratch using the ARM ELF manual
    (and the ARM Architecture Reference Manual)

 2) Inserting an trampoline. We use the B (branch to address)
    which uses an offset that is based on the PC value: PC + imm32.
    Because we insert the branch at the start of the old function
    we have to account for the instruction already being fetched
    and subtract -8 from the delta (new_addr - old_addr). See
    ARM DDI 0406C.c, see A2.3 (pg 45) and A8.8.18 pg (pg 334,335)

 3) Allows the test-cases to be built under ARM 32.
    The "livepatch: tests: Make them compile under ARM64"
    put in the right infrastructure for it and we piggyback on it.

Acked-by: Julien Grall <julien.grall@xxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx> [for non-ARM parts]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
Cc: Julien Grall <julien.grall@xxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>

v2: First submission.
v3: Use LIVEPATCH_ARCH_RANGE instead of NEGATIVE_32MB macro
   -Use PATCH_INSN_SIZE instead of the value 4.
   -Ditch the old_ptr local variable.
   -Use 8 for evaluating the branch instead of 4. Based on ARM docs.
   -NOP patch up to sizeof(opaque) % PATCH_INSN_SIZE (so 7 instructions).
   -Don't mask 0x00FFFFF_E_ after shifting, instead mask by 0x00FFFFF_F_.
    The reason is that offset is constructed by shifting by two the insn
    (except the first two bytes) by left which meant we would have cleared
    offset[2]! - and jumped to a location that was -4 bytes off.
   -Update commit description to have -8 instead of -4 delta and also
    include reference to spec.
v4: Added Jan's Ack.
   s/PATCH_INSN_SIZE/ARCH_PATCH_INSN_SIZE/
   s/arch_livepatch_insn_len/livepatch_insn_len/
   s/LIVEPATCH_ARCH_RANGE/ARCH_LIVEPATCH_RANGE/
v5: Added Julien's Ack.

IHMO my ack should not have been retained given that ...

   - Rebased on "livepatch: Drop _jmp from arch_livepatch_[apply,revert]_jmp"
   - Added explanation for the usage of data cache and why we need to sync it.

... you also replace the clean_and_invalidate to the old_ptr by clean_and_invalidate to the new_ptr.

diff --git a/xen/arch/arm/arm32/livepatch.c b/xen/arch/arm/arm32/livepatch.c
index 80f9646..3f47326 100644
--- a/xen/arch/arm/arm32/livepatch.c
+++ b/xen/arch/arm/arm32/livepatch.c
@@ -3,28 +3,303 @@
  */

 #include <xen/errno.h>
+#include <xen/kernel.h>
 #include <xen/lib.h>
 #include <xen/livepatch_elf.h>
 #include <xen/livepatch.h>

+#include <asm/page.h>
+#include <asm/livepatch.h>
+
 void arch_livepatch_apply(struct livepatch_func *func)
 {

[...]

+    /*
+    * When we upload the payload, it will go through the data cache
+    * (the region is cacheable). Until the data cache is cleaned, the data
+    * may not reach the memory. And in the case the data and instruction cache
+    * are separated, we may read invalid instruction from the memory because
+    * the data cache have not yet synced with the memory. Hence sync it.
+    */
+    if ( func->new_addr )
+        clean_and_invalidate_dcache_va_range(func->new_addr, func->new_size);

The clean_and_invalidate on the new_ptr needs to be add back here and ...

 }

 void arch_livepatch_revert(const struct livepatch_func *func)
 {
+    uint32_t *new_ptr;
+    unsigned int i, len;
+
+    new_ptr = func->old_addr - (void *)_start + vmap_of_xen_text;
+    len = livepatch_insn_len(func) / sizeof(uint32_t);
+    for ( i = 0; i < len; i++ )
+    {
+        uint32_t insn;
+
+        memcpy(&insn, func->opaque + (i * sizeof(uint32_t)), 
ARCH_PATCH_INSN_SIZE);
+        /* PATCH! */
+        *(new_ptr + i) = insn;
+    }

here. See the comments on the ARM64 part (i.e patch #5).

 }

Regards,

--
Julien Grall

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