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x86/sev-es: Use __copy_from_user_inatomic() 

The #VC handler must run in atomic context and cannot sleep. This is a
problem when it tries to fetch instruction bytes from user-space via
copy_from_user().

Introduce a insn_fetch_from_user_inatomic() helper which uses
__copy_from_user_inatomic() to safely copy the instruction bytes to
kernel memory in the #VC handler.

Fixes: 5e3427a7bc ("x86/sev-es: Handle instruction fetches from user-space")
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org # v5.10+
Link: https://lkml.kernel.org/r/20210303141716.29223-6-joro@8bytes.org
This commit is contained in:
Joerg Roedel 2021-03-03 15:17:16 +01:00 committed by Borislav Petkov
parent 62441a1fb5
commit bffe30dd9f
3 changed files with 55 additions and 15 deletions
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2
arch/x86/include/asm/insn-eval.h
View File

@ -23,6 +23,8 @@ unsigned long insn_get_seg_base(struct pt_regs *regs, int seg_reg_idx);
int insn_get_code_seg_params(struct pt_regs *regs);
int insn_fetch_from_user(struct pt_regs *regs,
unsigned char buf[MAX_INSN_SIZE]);
int insn_fetch_from_user_inatomic(struct pt_regs *regs,
unsigned char buf[MAX_INSN_SIZE]);
bool insn_decode(struct insn *insn, struct pt_regs *regs,
unsigned char buf[MAX_INSN_SIZE], int buf_size);

2
arch/x86/kernel/sev-es.c
View File

@ -258,7 +258,7 @@ static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
int res;
if (user_mode(ctxt->regs)) {
res = insn_fetch_from_user(ctxt->regs, buffer);
res = insn_fetch_from_user_inatomic(ctxt->regs, buffer);
if (!res) {
ctxt->fi.vector = X86_TRAP_PF;
ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;

66
arch/x86/lib/insn-eval.c
View File

@ -1415,6 +1415,25 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
}
}
static unsigned long insn_get_effective_ip(struct pt_regs *regs)
{
unsigned long seg_base = 0;
/*
* If not in user-space long mode, a custom code segment could be in
* use. This is true in protected mode (if the process defined a local
* descriptor table), or virtual-8086 mode. In most of the cases
* seg_base will be zero as in USER_CS.
*/
if (!user_64bit_mode(regs)) {
seg_base = insn_get_seg_base(regs, INAT_SEG_REG_CS);
if (seg_base == -1L)
return 0;
}
return seg_base + regs->ip;
}
/**
* insn_fetch_from_user() - Copy instruction bytes from user-space memory
* @regs: Structure with register values as seen when entering kernel mode
@ -1431,24 +1450,43 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
*/
int insn_fetch_from_user(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])
{
unsigned long seg_base = 0;
unsigned long ip;
int not_copied;
/*
* If not in user-space long mode, a custom code segment could be in
* use. This is true in protected mode (if the process defined a local
* descriptor table), or virtual-8086 mode. In most of the cases
* seg_base will be zero as in USER_CS.
*/
if (!user_64bit_mode(regs)) {
seg_base = insn_get_seg_base(regs, INAT_SEG_REG_CS);
if (seg_base == -1L)
return 0;
}
ip = insn_get_effective_ip(regs);
if (!ip)
return 0;
not_copied = copy_from_user(buf, (void __user *)ip, MAX_INSN_SIZE);
not_copied = copy_from_user(buf, (void __user *)(seg_base + regs->ip),
MAX_INSN_SIZE);
return MAX_INSN_SIZE - not_copied;
}
/**
* insn_fetch_from_user_inatomic() - Copy instruction bytes from user-space memory
* while in atomic code
* @regs: Structure with register values as seen when entering kernel mode
* @buf: Array to store the fetched instruction
*
* Gets the linear address of the instruction and copies the instruction bytes
* to the buf. This function must be used in atomic context.
*
* Returns:
*
* Number of instruction bytes copied.
*
* 0 if nothing was copied.
*/
int insn_fetch_from_user_inatomic(struct pt_regs *regs, unsigned char buf[MAX_INSN_SIZE])
{
unsigned long ip;
int not_copied;
ip = insn_get_effective_ip(regs);
if (!ip)
return 0;
not_copied = __copy_from_user_inatomic(buf, (void __user *)ip, MAX_INSN_SIZE);
return MAX_INSN_SIZE - not_copied;
}