RE: [PATCH 3/6] x86/sev-es: Use __put_user()/__get_user

From: Joerg

Sent: 12 May 2021 08:55

From: Joerg Roedel jroedel@suse.de

The put_user() and get_user() functions do checks on the address which is passed to them. They check whether the address is actually a user-space address and whether its fine to access it. They also call might_fault() to indicate that they could fault and possibly sleep.

All of these checks are neither wanted nor required in the #VC exception handler, which can be invoked from almost any context and also for MMIO instructions from kernel space on kernel memory. All the #VC handler wants to know is whether a fault happened when the access was tried.

This is provided by __put_user()/__get_user(), which just do the access no matter what.

That can't be right at all. __put/get_user() are only valid on user addresses and will try to fault in a missing page - so can sleep.

At best this is abused the calls.

David

Fixes: f980f9c31a92 ("x86/sev-es: Compile early handler code into kernel image") Cc: stable@vger.kernel.org # v5.10+ Signed-off-by: Joerg Roedel jroedel@suse.de

---

arch/x86/kernel/sev.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c index 6530a844eb61..110b39345b40 100644 --- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c @@ -342,22 +342,22 @@ static enum es_result vc_write_mem(struct es_em_ctxt *ctxt, switch (size) { case 1: memcpy(&d1, buf, 1);

• if (put_user(d1, target))
  

• if (__put_user(d1, target))
  goto fault;
  

  break; case 2: memcpy(&d2, buf, 2);

• if (put_user(d2, target))
  

• if (__put_user(d2, target))
  goto fault;
  

  break; case 4: memcpy(&d4, buf, 4);

• if (put_user(d4, target))
  

• if (__put_user(d4, target))
  goto fault;
  

  break; case 8: memcpy(&d8, buf, 8);

• if (put_user(d8, target))
  

• if (__put_user(d8, target))
  goto fault;
  

  break; default:

@@ -396,22 +396,22 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,

switch (size) { case 1:

• if (get_user(d1, s))
  

• if (__get_user(d1, s))
  goto fault;
  

  memcpy(buf, &d1, 1); break; case 2:

• if (get_user(d2, s))
  

• if (__get_user(d2, s))
  goto fault;
  

  memcpy(buf, &d2, 2); break; case 4:

• if (get_user(d4, s))
  

• if (__get_user(d4, s))
  goto fault;
  

  memcpy(buf, &d4, 4); break; case 8:

• if (get_user(d8, s))
  

• if (__get_user(d8, s))
  goto fault;
  

  memcpy(buf, &d8, 8); break;

-- 2.31.1

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